PVC and butane would scare the hell out of me. I used a 2" polyethylene tube and never ever run more than one 10 oz can of butane at it. I do it outside, away from any structures and fill it, leave it and come back in 1/2 hour. Do this before you partake that day. No stoner mistakes allowed. You are basicially making a pipe bomb. I gas leaking pipe bomb! The more I think about this the less I want to do it again.