I just picked up a Craftsman 2-1/2 gallon paint tank on Ebay for $10. I want to use it as a pressure pot for resin casting. The Sears tank looks a lot like the casting pots that cost around $250 and only require 1/2 the pressure. I don't know much about air tools. The tank has a regulator and a gauge, but I think I need some kind of on/off valve to fill the tank. Can I just using a plumbing fitting or do I need something specifically for air?