A month or so ago I picked up some steel food grade barrels and am just now getting around to setting them up as rail barrels behind my garage roof, my end goal is to have 12 of them lined up to supply water to the garden, most people gasp at the idea of 12 rain barrels but with my 20x25 foot garage roof they will be filled with around two inches of rain and my soil is mostly sand so it can soak up alot of water.
My goal was to have them all fill and empty at once while staying within a reasonable budget, I also wanted to have decent water flow out of the garden hose so that means large enough pipe, full flow valves and the barrels up high enough to get slight water pressure and on a slope to be sure that my valve to the hose was at the lowest point, of course I also wanted to make sure that I made the most out of what I have so I didn't want one barrel to over flow while others still had space, all of this provided a nice challenge for the day.
First thing was finding a full flow valve, I tried a normal garden hose spigot and it failed, it had enough changes in direction inside that the water with gravity feed would dribble out, but a valve that is normal used for natural gas supply piping was around $5 and was a full open quarter turn ball valve, perfect!
The next thing was how to fill it without getting grit in to it, being able to clean the grit off the screen without taking things appart, not having water spill all over the place and still allowing the water to over flow in a controlled manner, after all I went to the work of putting up gutters so why have the water spill on to the ground right next to the garage where it will soak in and cause problems.
In the photo I don't have the over flow pipe hooked up to the "T" but you can see how it would work once the barrels are full to the opening in the "T", of course I needed to keep the air venting out so they would fill but not allow the water to spill out of the top vent hole once they are full to the top so I have a foot high vent pipe on each barrel, both the 3/4" hole and the 2" hole in the barrels use standard pipe thread or plastic adapters work well as would iron threaded pipe.
so far it has been working well, I only have 3 of the hooked up due to it getting dark but it rained shortly after and quickly filled all 3, a little more time working on it and another trip to the hardware store and I'll be done, 660 gallons of rain water should help keep the garden green in mid summer.