
BARREL OVERFLOW SYSTEM (figure 1):

Figure 1
Next, I determined where I wanted to locate the barrel-overflow elbow. Most of the plans I found online used a simple fill-line process of locating the barrel-overflow at the top of the barrel. This is a pretty simple design – when rainwater in the barrel reaches that height, the additional rainwater just pours out the opening. I decided I wanted something a bit more useful and sophisticated on my barrel, so I put that opening at the bottom.
Let me explain my rationale – I wanted a fill-gauge on my otherwise opaque barrel, so I decided that if I put a hole at the bottom, plumbed some clear plastic tubing up the side of the barrel, and then trained the water over a U-shaped bend near the top of the outside of the barrel I could accomplish the same thing as the other designs, but with the added benefit of knowing how much rainwater was in my barrel at any given time. In addition, I have an overflow system that pulls from the bottom of the barrel instead throwing off the fresher water at the top (thus improving in-barrel circulation). From my short time as a marine aquarist I had learned a thing or two about plumbing and knew what I would need while I was at the hardware store.
At this point I drilled another hole near the back 1/3 of the barrel at the same height as the spigot on the front, again perpendicular to the curve of the barrel. I caulked and threaded the zinc elbow (male end) into barrel until it was snug and facing upwards (female opening pointing towards the top of the barrel). I ran another thin bead of caulk around this to ensure no leakage.
Into the female opening of the elbow I caulked and threaded the PVC coupling until it was tight. I pushed one end of the ¾” clear tubing over the barbed end of the PVC and slid a hose clamp over the barbed and tightened it. This next part is the tricky part, and you may wish to wait for this next step until the caulk has dried. I eyeballed the top of the rain barrel (estimating the thickness of the barrel top, the height of the bevel to the top of the barrel and roughly determined where the bottom of the lid to the barrel would be. I cut the clear hose about 2” longer than that length to start with.
Next, I fitted the two PVC elbows together over the male threaded ¾” coupling until I had a U-shaped bend. The plan is that the clear tube slides over the barbed end on one side of the U-bend and then I position it at the perfect height in relation to the barrel to provide the most amount of rainwater to collect without being so high that water overflows out the top of the barrel. Once I found the right height of the U-bend, I took the 1” copper hose stabilizer and secured the U-bend near the top of the tank. Then, I was able to more-accurately estimate the proper amount of clear tubing to trim off. I trimmed the clear tubing, slid a hose clamp onto the tubing, fitted the tubing over the barbed end of U-bend, and slid the clamp in place and tightened it.
THIS NEXT STEP IS CRUCIAL! You should drill one or two 1/8” (or smaller) holes in the top or outward edge of the U-bend. These will aid in breaking any siphon that forms when the overflow begins doing its job – due to the overflow location at the bottom of the barrel, a siphon would mean that your whole barrel will completely drain!
After drilling the holes, I added the first 10’ length of sump pump hose to the out end of the U-bend by puncturing two little holes in the end of the hose on either side. I threaded galvanized wire through the holes and around the end of the U-bend to hold the hose in place (see figure 2).
Now with the overflow in place, I filled the barrel to check my work. Once the barrel filled near the top (eyeballing from the opening at the top of the barrel, and following along with my clear-tubing-gauge on the side) I waited to see where water came out first – the overflow or the top of the barrel. To my delight, it began trickling out the overflow, and then flowing at a pretty good rate.
At this point, I decided to stain my barrel with a good outdoor wood stain. This is an optional step, but I did it to protect the logo of the whiskey company and ensure it sticks around for years to come. I also stained the half-barrel base for continuity. I applied two coats and let them dry thoroughly.
Next, I positioned the barrel on the stand and turned the barrel so the spigot faced the optimal direction for access to fill my watering cans and such. Then I ensured the opening at the top of the barrel lined up with the downspout location. A few minor adjustments to the base and I was ready to continue.

Figure 2