I dug out a 1 to 2 inch deep trench of the cooler's foam insulation all around the drain hole between the cooler walls, and used plumber's epoxy putty to cement in the correct-sized pipe nipple for my bulkhead, using a 1/2" ss ball valve connecting inside to a straight Bazooka Screen.
It is bulletproof drip free and completely solid in place, and drains like a champ. The existing drain hole was fine on my 70-quart Coleman Extreme (I do 10-gal batches), and drains the cooler mashtun completely, when the cooler is propped up at the opposite end towards the end of runoff.
I bought 3 different length pipe nipples in advance to make sure I got one that fit the best upon inspection.
