When welding fuel tanks, etc., I always fill with water, then tilt the tank so weld area is just above water line. Alcohol rinse tank mixes with any remaining water, removing all traces.
Ed
My dad did that years ago, blew himself out of the garage! I like Jerry's idea of filling with exhaust gas or ever putting dry ice in it to get rid of oxygen. Too much oxygen in water! (although I am too chicken to weld on a gas tank myself!)
