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Install a Rainwater Tank – 1200 gallon

By August 6, 2020August 31st, 2020No Comments

I install a 1200 gallon (4550 litre) rainwater tank to collect water for our garden when our irrigation well gets low in the summer.  This is three part mini-series.

See the Youtube Video Part 1 or  Youtube Video Part 2 or  Youtube Video Part 3

Install a Rainwater Tank – PART 1: the Base

(this is a transcript from the video)

Even after we had 5 feet of mud removed from our shallow irrigation well, it still runs dry in the middle of summer. It’s definitely better than it was, but to expand our garden we need more water.

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Last year we bought two rainwater tanks, a 1200 gallon, and a 500 gallon. In this series I’ll go through all the steps I took to install and connect this first tank to the gutters of these two workshops.

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In the following series I’ll look at the smaller 500 gallon tank that we installed off-grid in the garden and powered the pump with solar. So that’s coming up a bit later.

So, in this first episode I’ll go thru building a solid foundation to support the weight of all that water. In part 2 I’ll connect the tank to the roof gutters. And in Part 3 I’ll detail how I build the fence that surrounds part of the tank AND cover connecting the tank to a pump to feed our garden system.

Our property is on Vancouver Island and we get a lot of rain in the winter but the summers seem to be getting drier and drier. We need enough extra water on hand to make it through July and August mainly. So, we estimated that this 1200 gallon and the other 500 gallon tank would be just big enough to cover that dry spell. Drawing from these tanks for part of the time should give the shallow irrigation well some time to recover.

I’ve never installed a rainwater tank beyond a 55 gallon poly drum before so I was learning as I was going along. There’s a lot of great info online for installing tanks. I really like the video Frank Howarth did a few years back on the tank he put in beside his shop.  I can now totally relate to his experience and how long it took him, thinking through the process, before drilling his first hole in the tank.

Our property has a gradual slope and there’s no truly flat spot for this tank. I wanted to instal it on the downslope side of these two workshops and draw water from their combined roofs. And given the height of the tank and the height of the gutters we found the best spot just off the corner here.

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We needed to build a solid, flat base for the tank that also drained well. Water coming off the top of the tank runs down the sides and may erode the base material. So that was a consideration in the design of the tank foundation. I decided to pour a low concrete curb to hold the gravel and also to support the fence later.

I have several other projects on the go this summer that require a low concrete wall so I can reuse the forms. For me, it made sense to invest the extra time and expense to pour concrete for this.

I set the tank where I thought it should go and marked lines on the lawn.

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This tank is not heavy but large and awkward. Works best to roll and lift a bit at a time. With a spade I cut the sod into a grid of square sections.

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Then removed the sod and topsoil to create this flat, level spot.

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It took a few hours and a lot of wheelbarrow trips for Marilyn, but it was a really good workout.

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A 5 inch wide by 8 inch high curb will be poured here. Then filled with gravel.

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And the tank will sit on that.

Beside the tank there’s a perforated pipe about a foot underground that’s surrounded by drain rock.

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We dug that in a few years ago to help with drainage behind the shed and workshop.

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As I’m essentially creating a bathtub with the concrete curb, I’ll need a path for the water to flow away. I wanted to add a short length of pipe to direct the water from under the tank to the drain rock surrounding that existing pipe. I dug a trough and lined it with drain cloth, added some gravel, then the pipe, more rock.

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Then topped it with more fabric and rock.

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I made the forms from 1×8’s. They will be held in place with 1×2 stakes. Temporary 5 inch blocks help with spacing the inner and outer forms. More stakes are driven in and then the blocks removed.

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I attached 2×4’s to these boards to screw the stakes to. I’m not a forming contractor and I’m sure there’s a simpler way to do this but, this is what works for me.I roughly position the outer forms and clamp the corners together. Then run in some screws. This worked well to create the basic box. Then I squared and levelled it as I was driving in stakes to hold it in place.

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It’s funny what you discover when you film yourself working on a project. I seem to have a furniture or woodworkers approach to what is really rough carpentry. I’m not a carpenter or a builder. I simply have a passion for building things. And, I don’t have an issue at all with constructive criticism or tips from you builders out there. We can all benefit here so I welcome your feedback.

With the outside form boards in place I can make the inner walls that will create the curb. I wasn’t sure how well the forms would come apart on the inside as I was worried that they would bind against each other.

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So I made the inner forms walls in two pieces. I cut the end off the inner form wall at a 45 degree angle on one end.

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Then I reattached it with a mending board.

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I figured this will make stripping the forms easier as this piece can pivot away from the corner. I’m not sure if I really needed to build them this way but it only took a few minutes to do this.

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This idea came about as I was working on a square concrete planter form. It seems that it can be challenging to disassemble the inside of a closed space. More on that project in a future video.

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I clamp and screw the inner forms together. And attach the 5 inch spacer blocks. That worked great. It help suspend the inner form at almost level as I pounded in the stakes. I ended up using two blocks at each corner.

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Once these were removed I coated the inside of the form with vegetable oil.

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I bent four 10 foot lengths of rebar, wired them together and suspended them from wire so they would stay in the center of the curb during the pour.

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Now it’s a matter of loading the concrete mixer and filling the forms. My little mixer can handle 2 bags at a time.

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To save my back I have the bags stacked at the end of my pickup box. I add some water, set the bag over the drum and cut it open to dump it in. Then start the drum spinning before tilting it. When this is mixed I do the same with the second bag.

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After a few minutes I rotate the drum over to the other side and dump it in a wheelbarrow.

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The curb is narrow so I opted to fill the forms by hand with a shovel instead of just pouring the concrete right out of the wheelbarrow. Given the slope and access, I decided I’d spill a fair amount of the wet concrete so, shovelling would take longer but waste less. And this worked well.

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Marilyn came to give me hand and that went much faster. We got into a flow and the pour went much faster than I expected. I loaded the mixer and Marilyn filled the forms.

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Before the concrete hardened I added some anchor bolts for the post brackets. And covered the fresh concrete with plastic.

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After a few days I stripped the forms. And this went well. The outside boards came off without any problems. And the inside ones as well. The curb looked great. I kept it covered with plastic to cure for a while longer.

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I’ll be installing a pump in the shed beside the tank so I roughed in a 1 inch water line that drops under the curb and over to the wall of the shed. More on that in Part 3 of this series.

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I rolled out some drain fabric and shovelled in a layer of crushed road base. Raked this flat and packed it down.

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Then I topped up the base surround with 3/8″ pea gravel. It’s a finer round rock that drains well and has no sharp edges that could puncture the tank. The pea gravel does not pack so well so I added some sand to it. And that seemed to help.

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With the gravel level and packed we slid the tank into place. We used some 2 by fours and a strap around the tank to help with this. It was satisfying to finally get the tank into place.

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Install a Rainwater Tank – PART 2: the Plumbing and Tank Fittings

(this is a transcript from the video)

This is part two of my series on installing this 1200 gallon rainwater tank. It the first episode, I excavated a level spot beside this shed and poured a curb to hold the gravel that supports the weight of the tank AND allows water to drain from around the tank without causing erosion.

In this episode I’ll show how I connected this tank to the gutters.

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To get the most water I can in our dry summers, I connected the gutters from the larger workshop to this shed and that gave me about 1400 square feet of roof.

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A few years ago I installed a steel roof on these buildings and added new gutters that have a leaf guard.

Because of that I won’t need to add a leaf screen to the downspouts. And that’s good because I don’t have a lot of distance from the bottom of the gutters to the top of the tank.

I have just enough space for pipe slope so I can connect BOTH sides into one. In the winter when we get heavy rains I can remove the pipes that connect the gutters between buildings and reinstall the aluminum downspouts.

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I replace the downspout on the shed here with 3″ PVC drainpipe. I added a gate valve for water collection in the summer. I close the valve and water backs up and fills the first flush diverter then runs around the building to the other side.

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On the opposite side of this smaller workshop I’ll put together another pipe and fitting assembly as the first one.

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The gate valve and the “T” at the top of the first flush diverter are designed to fit a Schedule 40 PVC pipe. That’s a thicker walled version of the 3″ drain pipe I’m using for everything else. So I need to first glue in these sleeves to allow me to connect everything together.

I could only find the black ABS sleeves but they will work fine for this. I just need the right glue that works on PVC and ABS together. And you have very little time, a few seconds really, to get the parts in the right position once you glue them and slide them together. And there’s no going back for a second try.
So planning is key to making this work. I dry fit everything first and use a sharpie to mark what goes where. Except, the morning I was working on this assembly.

I work as a Paramedic and my schedule is erratic and not always consistent. I worked a night shift and didn’t get enough sleep in the morning, then tried to do some plumbing. Not a good combo.

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I glued the sleeves into the “T” at the top of the first flush diverter and that was okay. But, right there is the problem.

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For some reason I was thinking that the “T” that sits above the gate went in the same orientation as the first flush T. And I went ahead and glued them together.

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And that’s the moment right there that I realized what I did. And then some choice words came out of my mouth.

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Cause the first flush T is a specialized part that I ordered. And getting a replacement would put me back days and days. And there was rain in the forecast.

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Then I took a break to calm down. I realized to fix it I had to separate those two T’s.

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And as I mentioned the glue is unforgiving. I had to cut off most of the standard “T” and glue a new one on the first flush “T” on the other side. Later I’ll use a rubber coupling to adapt the messed up end of the first flush T to the pipe that heads to the tank.

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So now back on track, I assemble the rest of the parts in their correct orientation.

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This assembly is attached to a pipe that runs down the wall and into a 4″ drainpipe below ground and is loosely attached to the wall while I work on the section that goes from the gutter outlet to the first “T”.

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After that’s in place I added more straps to hold these pipes to the wall. And glued a section of pipe for the first flush chamber along with the threaded section for the cap and small drain at the bottom.

With the new downspout assemblies in place with the bypass gate valves and first flush pipes, it’s time to get the other parts of the tank ready.

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I bought some of the tank parts and decided to make some of them from existing fittings.

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The tank I bought has a 2 inch bulkhead fitting already installed. It’s for connecting more tanks together and for draining the tank quickly. Or, it can be used for drawing off water. I’ll be adding a float and screen to this tank so I can draw off the cleanest water that’s just below the surface and away from any sediment in the bottom.

So I need to add a ball valve to this existing bulkhead fitting. I first add a reducer down to one and a half inches. I didn’t have channel lock pliers big enough for these so I used a pipe wrench, which is overkill but worked. Then a short nipple, and then the ball valve.

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I cut this hose down to a length appropriate for the height of this tank. I guesstimated this. There’s a barbed fitting that goes into the inside part of the bulkhead fitting first.

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Then the clear flexible hose goes onto that. It was tough to get this on, even with some soapy water as a lubricant. Stainless steel hose clamps secure it. But, I’m sure that’s never coming off anyways.

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Then the screen and float goes on the other end. And a lanyard is tied to the float. This will keep the screen up off the bottom of the tank when the water level gets low.

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I’ll need to drill a hole in the tank for a bulkhead fitting for the hose that’s connected to this float. I’ll use a hole saw for this and position this hole 4 about inches off the bottom.

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Then, the challenge is to get this end through the hole in the tank. Thanks to a few other YouTuber’s (I’m looking at you Frank Howarth) the trick is to use some string. I taped it to a pipe then fed that through the hole. Then the other end is attached to the opposite barb.

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I now pull the string to bring the bulkhead fitting through the hole and attach the nut.

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I snug this up with pliers. I gotta say, there was some anxiety doing this. It felt pretty tricky the first time. But it went well.

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I’ll be connecting this fitting to the 1″ pipe that runs under the curb later.

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But for now I’ll add an elbow and a ball valve so I can make the tank now water tight. I detailed that in Part 1.

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On the other side of the tank I’ll add a gauge. It’s a float on a spring coiled spool that you set to your low and high water points. I added this away from the float to they don’t get tangled.

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To find the best spot for the tank inlet I sighted down a large speed square.

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I lined up one edge to the curb and marked the point where the 45 degree edge contacted the tank. That way I could use standard 45 degree elbows to connect the pipe to the wall. I wanted this hole as high up on the tank as possible. I need as much water in there as it hold.

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It took some planning, checking, and head scratching to be sure I had this right before I drilled into the tank.

Feeling confident, I used a large hole saw for the inlet and overflow pipes. On the slow setting, I drilled until the pilot bit pierced the tank, then clicked the drill in reverse to cut the big hole. This keeps the hole saw from grabbing. And it worked great.

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The rubber grommet fits in the hole and the pipe expands the rubber and make the seals waterproof. Well I hope, it certainly is very tight. And there won’t be much pressure at the top of the tank anyway.

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So water does not stir up sediment when the tank is filling, I’ll run a pipe to the bottom with two elbows to create a calming inlet. So the water fills the tank from the bottom and doesn’t splash. I glue up a 90 and 45 fitting and attach it to a straight pipe.

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Then set this in the tank and mark it on the down facing elbow. I cut this to length then dry fit it. I’ll attach these with a stainless steel screw instead of permanently gluing them.

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I cut all my PVC pipe on a 8″ compound miter saw. It’s fast and leaves a clean, square edge.

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For a lot of the sections of the plumbing here I tried to think about having to disassemble things later. So I only glued what I really needed to. And… maybe that’s just my lack of confidence.

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I like these 3″ flexible rubber couplings with the two screw clamps. They are great for quickly taking sections apart. And to manage tough connection points or those that require some flexibility. With my limited plumbing experience I need all the help I can get.

I made an assembly of pipe with a Y to finally connect the pipes from both sides of the building. And that has a 45 degree elbow before it runs into the tank. This part has 3 rubber couples so it went together without too much fussing. And I like that I can take this overhead part of the plumbing off the tank if I need to.

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For the tank overflow I’ll use standard fittings to create a siphon. It’s a series of 90 degree elbows and an angled pipe. When the tank is full this siphon will skim water off the surface and send it down a pipe on the side of the tank to the drain that runs out to the ditch on the road.

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On the end, there’s a screen to keep mosquitoes out of the tank.

You can buy a siphon formed from one piece but my suppler was out of stock. I think it might actually be cheaper than making your own when you add up the cost of the fittings.

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Now, I can drill the hole for the overflow siphon. It’s just slightly lower than the inlet hole. And I needed it to rotated around this access hatch wall so it didn’t run into the inlet pipe.

And I can glue that in place.

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Next I’ll tie the tether for the float to one of the pipes to keep it off the bottom.

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I’ll dry fit the overflow down pipe and temporarily secure it for now. I’ll set it in it’s final position when the fence surround is done.

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And shortly after that it started to rain. And water started to fill the tank.

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This occurred to me after I had put my system together and I realized this is something I should have tested first. So I put together a rig to see how much water might end up running over into the first flush chamber when the gate valve is open.

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There wasn’t a lot, so, I’m not too worried about that.

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In the winter when we get a lot of rain I’ll remove the float ball and slow release pin hole washer in the bottom of the first flush so water can drain quickly out the small clear hose into the 4″ drainpipe.

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I then swapped out the straight tee for a sanitary tee. It has a sweep or curved section and what I found was there was no water dripping from the horizontal pipe.

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So, if I was going to build my system again I would use the sanitary tees instead of the straight tees.

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Install a Rainwater Tank – PART 3: the Cedar and Corrugated Surround

So there’s the bare concrete curb filled with pea gravel.

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The fence surround is constructed from 4×4 posts that are attached to galvanized post saddles. (I embedded anchor bolts in the concrete for these saddles.) There are 5 posts in total.




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Between the posts I have a bottom rail made from a 2×6 then a mid rail and top rail made from a 2×4.

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When we poured the concrete curb I embedded some anchor bolts to hold these adjustable post saddles.

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I like these as they lift the post off the concrete by an inch.

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And they are slightly adjustable. I find that my anchor bolt placement can be off a bit so this really helps.

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After the design is done in Sketchup I can start cutting the parts. I have some cedar milled from trees that we fell on our property. These have been air drying for a few years. I had them milled full dimension and I really like the rough sawn look.

With a square curb I was able to design all the individual parts to be the same size. All the posts are the same length as well as all the rails are the same length. And this made cutting everything straightforward and pretty simple.

I cut all the 4 by 4 posts first.

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The post saddles are designed for a nominal 4 x 4 which is actually 3.5 inches square. So I need to trim down the bottoms of the posts.

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And I’ll break these wafer pieces off and finish with a chisel.

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Next I’ll cut the 2×6’s for the bottom rails. And then the 2×4’s for the mid and top rails.

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To flush mount the galvanized corrugated panels I cut a rabbet in the top and bottom rails. And I can use my portable table saw for this.

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With all the parts cut I roll on a coat of stain. This is a one coat Sikkens semi-transparent stain.

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The colour is called butternut. I used this same stain on the Garden Pavillion a built a while back. It’s pretty fast to apply it with a roller. I add a few extra coats to the tops and bottoms of the posts. And the ends of the rails.

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The next day I can start to put everything together. I’ll be toe screwing the rails into the posts. Good enough for what is essentially a fencing project.

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A single screw through the post saddle holds the bottom of the post in place while I clamp temporary braces to two sides. Then plumb the post with a spirit level. And I can repeat that on the second post.

Blocks clamped to the posts support the rails. And a long pipe clamp pulls the posts together as I run in the screws.

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Working my way down the post I’ll next add the middle rail. Again, blocks support the rail while I bring the posts together with a pipe clamp. And run in more screws. And more screws.

Then the 2×6 bottom rail can be added.

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I had my roofing supplier cut these panels to 5 foot lengths. And I designed the surround fence so the posts were set apart about an inch greater than the panel widths. So I didn’t need to cut any metal for this. And I like that.

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I added a corner brace between the mid rail to add some rigidity to the ends of the surround. If there’s too much movement I can add another brace to the top rails later. But I think it’s good enough like this.

The next day I added the panels. Eighth inch spacers lift the panel a bit to center it vertically. I used 1″ roofing screws that have a metal and rubber washer. This went quickly and I was done in less than an hour. I think taking the time to cut the rabbit in the top and bottom rails, so the panels are recessed flush, is worth the extra time. We though it looked pretty sharp.

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I covered all the tank plumbing in part 2 of this series but I forgot to add a vent.

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For this I bought an RV tank vent and fitted it with a bug screen. I cut a disc of aluminum window screen and siliconed it to the base of the vent.

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I cut a hole in the top of the tank with a hole saw. Added some silicone to the base of the vent and attached it with screws.

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Drill hole for vent

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Silicone on base of RV vent

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Screws hold vent onto tank

Our shallow irrigation well is over in this corner of the property. It has a water line running under the field toward the house and past this shed. A few years ago when we put in the garden I tied into this line and installed several hose bibs.

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I have a pump to pull water from the rainwater tank and send it to the garden. The plan is to turn off the well pump and close it’s ball valve. Then turn on the tank pump. So it can take over watering when the drip irrigation timers come on in the garden.

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The pump will be set up in the shed on the left there. And I’ll run a 1″ water line underground and tie into the garden system. I ran a string line between two stakes to mark my trench location.

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I cut the sod with a spade. And enlisted some additional help on the other side of the fence by the garden taps.

I have to get down to the poly line to see how I’ll tie in the rainwater supply to it.

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There’s nothing like digging to remind yourself that you are out of shape and need to up the cardio in your workouts.

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In part 1 I roughed in a 1″ white PVC line under the curb and to the corner of the shed. I’ll now continue that line up and through the shed wall. This is the supply line from the rainwater tank.

A galvanized strap will keep it secure for now.

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Where this line comes up through the pea gravel I’ll add an elbow and barb fitting. Then I’ll connect this to the ball valve at the bulkhead fitting with some flexible black poly pipe.

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Next I’ll add the line that comes out of the shed from the pump through the wall. This will have a tap on it as it continues down the wall and underground.

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Now it’s a matter of wrangling a roll of poly pipe into the trench. I’ll rough cut it to length and lay it in.

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I’ll cut the existing supply line that comes in from the irrigation well and add a T. It’s a bit of muscle work to get it all to fit before I squeeze the poly pinch clamps.

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Working the T onto the existing pipes

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Then on the shed side I run the poly pipe into the other barbed fitting and clamp it. All the outdoor plumbing is done.

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I bought a half horsepower jet pump with a small pressure tank attached. It came with a 20/40 pressure switch. On at 20 psi and off at 40 psi.

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I’ll swap that switch for a 30/50 with a low pressure cut-off. This will stop the pump if the tank runs dry or the pressure drops below 20 psi.

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I’ll disconnect the wires then spin the switch off the pump housing. I’ll add a short nipple as the new switch does not come with one.

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Adding 1/4″ nipple to pump housing

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Since this is a season pump setup I opted to wire a 110 volt plug to the pump. So I can just plug it into a receptacle in the shed when I need it.

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So here’s a schematic type layout of how I’ll plumb in this pump in the corner of the shed. The bottom line comes from the tank, and the top line goes to the garden.

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I’ll add compression couplings and unions to aid in the initial glue up of the pipe and fittings. And to allow disassembly and draining of the system later. I also have a check valve so water can only flow from the tank and never back to it.

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Coming out of the pump I’ll add a pressure gauge, a ball valve, a spin down sediment filter (to catch any debris from the tank), then another ball valve.

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And here’s the system installed in the shed. I did add another check valve to ensure I kept water from ever backing up into the pump when I’m switching from irrigation well supply to rainwater tank supply.

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I’m not a plumber but I think this will work okay.

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So I hope you have enjoyed this post, and thank you so much for reading. If I make any further improvements or changes I’ll post them here.

And, while you are here, please hit the Support Link to help us make more projects and videos like this. We really appreciate anything you can do to help us out!


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