I used to have a glass downtube, but the cats managed to knock the entire bucket of water over. We're talking 5 gallons, and a 10lb (if that?) cat. Needless to say, the downtube when 'shatter'.

So now I use a copper tube. If you look carefully in the video, he has a copper tube as well. There was a link to a "How to Build It" step by step.. But I can't find it. It's probably somewhere on the video link.

Eh.. The smoke isn't too bad with copper. Not as good as with glass, but it does the trick.