I have just completed a forge made from a 20lb gas bottle, 3" ceramic fibre all around the inside and 2" lining the "porch" with a fire brick floor, the burner is 3/4" pipe with a 1" reducer as flare inside the forge, the plumbing is a bit of everyones ideas to work with stuff I had on hand, basically it is a 1/4"nipple brazed into a 3/4" pipe ...