Installing a drain valve in a plastic barrel allows you to easily access whatever liquid you have stored in the barrel. The most common reason for installing a drain valve in a plastic barrel is when you are using the barrel to collect rainwater. Rain barrels have a drain valve on the bottom of the barrel so you can hook up a garden hose, or simply empty the barrel by opening the drain.
Remove the lid of the plastic barrel and lay the barrel on its side. Select the location for installing your drain valve. If you are constructing a rain barrel, select a spot 2 to 3 inches from the bottom of the barrel.
Insert a 1-inch drill bit into your electric drill and drill a hole through the spot you selected.
Screw the threaded end of a plastic drain through the hole. Remove the plastic drain valve and wrap the threaded end in 2 layers of Teflon tape.
Coat the threaded end in waterproof caulk and screw the drain back into the hole. Let it sit overnight.
Apply a thread of caulk around the valve where it meets the barrel, both on the inside and outside of the barrel. Let it dry for 24 hours.