Step 4: Fluid Release Systems
The obvious way to release pent up water is to have a hose and hose bibb at the bottom of the second barrel. REMEMBER KIDS: water flows downhill, therefore, make sure barrel two is DOWNHILL of barrel one. this allows them to both fill and for water to come out of the hose when you want to water something.
These barrels are quite thick. I placed the bibb at the bottom of barrel 2 about 4in off the ground. Low enough to get most of the water out, high enough to keep the hose from kinking. I drilled a 1/2in hole in the side of the barrel and slowly dremeled the hole wider until the brass fitting cut its own threading into the plastic, leaving me with a strong, watertight seal. It's key not to ream this hole too large or you'll have a leaky bibb.
Do the same thing up top for your OVERFLOW. Overflow is important. 1in of rain on a 1000sqft roof will give you about 623 gallons of runoff. since my gutters cover 1/2 of my roof footage (about 1200 sqft) I anticipate these barrels being full at some point. When that happens I want to make sure the excess water heads out to the street to the public drainage system. Drill a 1 3/4 in hole in the top side of the barrel and ream until the PVC fitting will cut a thread in the sidewall to create an overflow.