Adding rainwater harvesting to my Costco greenhouse seemed like an excellent idea because I want to reduce my dependence on the garden hose. Friday I installed DIY greenhouse gutters, and today I finished linking four rain barrels into a simple catchment system.
In a perfect world, this would have been done yesterday but technology steered me all the way wrong on my parts list. I’m listing the correct materials here so you can avoid that frustration.
Materials list for this project:
- 4 food grade 55 gallon drums
- 8 concrete blocks
- 16×16 concrete pavers – 4
- 3/4″ bulkhead fittings – 6
- Brass Hose Barb Fitting, 3/4″ Barb x 3/4″ NPT Male – 6
- 3/4 braided PVC tubing
- 25mm – 38mm thumb screw hose clamps
- Brass Hose Bibb, Heavy Duty 3/4″ Male NPT * 3/4 GHT Male – 1
- Silicone sealant
- Screening
Tools:
- jigsaw
- step bit (unibit drill bit) – make sure there’s a 1 1/2″ step bit because that’s what fits the bulkheads I linked. I learned this one the hard way
- power drill
- vise grips (locking pliers)
Let’s talk about step bits!
I didn’t know anything about them before this project. A step bit (also called a unibit) is a cone-shaped drill bit with multiple cutting diameters built into one tool. Each “step” enlarges the hole slightly, so you drill until you reach the size you want.
They’re especially useful for plastic, thin metal, and PVC, where regular drill bits can grab or crack the material. Step bits leave clean, smooth holes, which makes them ideal for projects like installing bulkhead fittings in rain barrels or drilling holes in greenhouse parts.
I ordered step bits online since local prices were ridiculous — about $50 and up for a single bit — and the local selection was basically “this is what we have, hope it works.” I got a set of five for about a third of the cost of one purchased locally. They were supposed to be here by 8 am Saturday morning.
They arrived at 7:15 pm Saturday night.
Make sure the set you buy includes a 1½-inch step. Mine only went to 1⅜ inches, which technology assured me was correct. Spoiler alert: It was not. I made it work, but having the correct step bit from the start would have made this a simple case of drilling one hole instead of drilling one hole and then futzing around to add another 1⁄16″.
Prepping the Rain Barrel Bases
While I waited for the bits to arrive, I busied myself with other prep work. I bought four 16×16 concrete pavers and leveled those. Then I placed two concrete blocks side by side on each paver and leveled those as well. I stood the barrels up, and tried to level those and that is where things went a little sideways. They’re straight now, even though I know this photo shows that first set looking all the way wrong.
Preparing the Bulkhead Fittings
Next I organized the plumbing hardware.
I located the bulkhead pieces. The bulkhead fitting passes through the wall of the barrel. The bulkhead comes with a rubber gasket and a locking nut. The gasket goes on the bulkhead before it is pushed through the hole, and then the locking nut is tightened from the inside to compress that external gasket and create a watertight seal. The brass hose barb fitting will screw into the bulkhead and the flexible hose is pushed onto the barb.
The brass hose barb threads need to be wrapped in Teflon tape before being screwed into the bulkhead. Teflon tape is a thin white tape that wraps around threaded fittings. It fills small gaps in the threads and helps prevent leaks. It also prevents your threads from seizing up. I wrapped two or three rotations and then pressed it into the threads with my fingers. Ignore what I did here, because the Teflon tape should stop before the top threads. I redid it but didn’t take a photo.
Then the brass hose barb is screwed into the bulkhead like so. I did four of the six needed, and they’re ready for installation! The flexible hose goes on the barb, and I have hose clamps to seal that even further.
I marked the holes that I’ll need to drill. These barrels are food grade and have a handy gallon measure on the side. This made it very easy to mark consistent holes in the barrels. The first barrel needs one hole, and that is the intake barrel from which the water will flow into the other three. Barrels two and three have a hole on each side, to make the connection. Since these barrels are cast molded, it was easy to make a corresponding hole on the opposite side by following the molding seam. Barrel four will have one hole to receive the last connection.
Barrel four will have a bulkhead higher up on the other side, because that is where I’ll be putting a tap to draw from the tank. Later I decided that if I was installing one tap, I might as well install another on barrel one so I have access to water from both the east and west sides of the greenhouse.
At this point I was getting a little irritated that the bits weren’t here yet, so I decided to cut my screen holes in the top of each barrel. Let me assure you of this, friends, HDPE plastic in a food grade barrel is THICK. I spent all afternoon trying to get it handled with zero luck, a couple of cuts to my hands, and then I threw a pair of vise grips into the yard. I asked my good friend JD Hanley if he had a jigsaw I could borrow. Not only did he have one, he had an extra, so now I own a jigsaw!!
A jigsaw made short work of the circular holes. I used a marker to draw a six inch round hole in the top, and then drilled a pilot hole. Jigsaws work by moving a thin toothed blade up and down rapidly. There’s a flat shoe that guides this action, and once I got that settled, the cutting went quickly. Side note – I learned that I cannot get my arm into a six inch hole. Your mileage may vary.
I cut this hole for a couple of reasons. First, it will allow me to reach into the barrel to screw the locking nut and gasket onto the bulkhead from the inside, as I mentioned above. Second, it will make cleaning the barrels and fishing any debris out much easier. I’ll screen these holes to make certain that mosquitos can’t make my water catchment system a sexy rumpus room. Nobody enjoys Zika.
Installing the Bulkheads
Now that I had the step bits, I hit the ground running on Sunday morning. Once the holes were drilled, I placed the rubber gasket onto the bulkhead and pushed the threaded flange through the hole. To install the locking nut, I sat in a chair and turned the barrel sideways, resting it against the trash can so it wouldn’t move while I shoved my arm through the top opening.
Let me tell you something right up front. When you think you have hand tightened it as far as you can, put all your mustard on the bread and force it a little bit more by hand. No need to get a wrench and overdo it, but definitely put a little extra power on that final turn.
I’m sure I was a sight to behold, squatting on a chair, arm deep in a barrel, my cheek pressed against the barrel top while I tried to get the nut on the flange by feel alone.
Once I had four of the bulkheads installed, I ran a bead of silicone sealant around the top opening, pressed the screen into it, and then ran another bead over the top. That seal should cure waterproof and weatherproof while still staying flexible enough to survive freeze/thaw cycles.
This is where I had another learning moment: Don’t install the screens until after you finish leak-testing the bulkheads. You’ll see why in a moment.
Connecting the Barrels
I cut the flexible hose in four long-ish pieces to push onto the hose barbs and secured it with hose clamps on either end. You’ll end up with a loop between each barrel, and that is how it should go. My first cut was a very short run, and then I couldn’t push the hose onto the second barb because I had no play left in the hose.
Another learning moment: wait until you have leak tested your bulkheads before you affix the hose and clamps. If your bulkheads fail the leak test you’ll have to go back and unhook them to get into the barrels to tighten the locking nuts.
I had the help of my dear friend The Water Fairy to help run the hose while I inspected my gutter connections, downspout aim, and bulkhead tightness. Here she is, sprinkling my roof quite beautifully!
Oh, I was so excited to see the pitch of my gutters was working properly! Those DIY greenhouse gutters I installed the day before were doing exactly what they were supposed to do.
Unfortunately, I failed the leak test.
The Water Fairy took me out for an early dinner and cheered me up considerably. When I got home, I had to buckle down as I was losing daylight and I wanted those bulkheads to pass the leak test TODAY!
Since two of the barrels were up on concrete blocks and half full of water, I tried to get up on a steplader to reach down into the water to tighten the bulkhead nut. This involved removing the screen I’d already installed. I still couldn’t get down to the nut. I unhooked the hoses connecting the two half full barrels to empty them, and that wasn’t going very well, so I used my rage constructively and hurled the two barrels to the ground while exercising some creative and colorful invective as to how I got into this predicament to begin with.
I unhooked the remaining barrels and rolled them into the garage, repeated the whole squat, reach, cheek press, feel for nut process, and here again, my annoyance strengthened me: those nuts are absolutely hand-tight and more, and passed the leak test.
You’ll see here that I learned quite a bit by failing the leak test.
- Don’t screen the openings in your barrel tops until you know your bulkheads do not leak.
- Hand tighten the locking nuts, and then hand tighten them again.
- Don’t connect your hoses and clamps until you know your bulkheads do not leak.
I hooked the whole array back up and now I have a rainwater system for the ages. Or, I will tomorrow once I get the taps in, but that should be a problem free process of Teflon-taping the tap threads and screwing the tap into the bulkhead. I’ll leak test those fittings with the hose, and THEN I’ll replace the screens on the barrel tops, just in case I have to get in there again.
How Much Water Can the Greenhouse Collect — Is It Worth the Angst?
A handy rule for rainwater harvesting is that one inch of rain on one square foot of roof produces about 0.62 gallons of water.
My greenhouse is 8 × 10 feet, but the barrels only collect runoff from one side of the roof, so the catchment area is about 40 square feet.
That means every inch of rain should produce roughly 25 gallons of water flowing into the system.
In my area of Michigan, a typical summer storm often drops about ½–1 inch of rain, which means this system could collect 12–25 gallons from a single storm.
With four linked barrels the system holds roughly 220 gallons of rainwater, which should go a long way toward keeping the raised beds watered without dragging the hose around the yard.
Considering how much attitude this project gave me along the way, I’m going to call that a fair trade. I can only hope this post saves someone else a few of the DIY headaches I ran into.
The Amy Experience 
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