where did you get that petcock at zrtmwa? I think that is what I need...On my mountain bike the top tube is the same size all the way up, so big I can't even use the bolts and clamps that came with the tank (JB Weld or Duct tape?). The washer method worked for my petcock.
You could probably use JB Weld or buy a 90 degree petcock too, like this one (fuzzy image):
Q