Old fire extinguisher works great. If you use the exit valve for the incoming line.The intake line is made of stainless with a diffuser built in. Caution, you must keep the bubbler at least 75% full. Have 4 to 6 in. from the top,the closer to the top the less gas there is and when it blows it won't be real bad.. Or, you will be playing with dynomite!! There is only a little drilling and tapping to do.This bubbler will require a substantial amount of pressure from HHO. As long as the output stays 4-5 inches under water the size really isn't the important. I've had them blow up big time. Was using PVC 4 inch. Made one heck of a bang. Didn't have enough water in it. I'm using a 2 quart juice jug so if it does blow it won't do much more than blow off the top and I can SEE what's going on in it. If you are using anything that you can't see the water level a level tube needs to be used. Bubblers are very important, I've blown up generators.