Once again

"PVC contains 56% chlorine. When burned, PVC produces large quantities of hydrogen chloride gas. When breathed, this gas combines with water to form hydrochloric acid in the lungs. Dioxins and furans can also be produced. "

" It only takes five ounces of burning PVC to give off enough hydrogen chloride gas to kill the occupants in an average size bedroom in ten minutes"

Not trying to be an asshole, just stressing that PVC fumes are bad news. I've done a lot with PVC and sometimes I heat it up to make it bendable. I can tell you from experience that it doesn't need to look melted or burned to be giving off fumes. Whenever I'm heating it I always wear a mask and do it in an area that's well ventilated.

Bottom line, PVC is not meant to be used as a matarial for a smoking device. Don't risk it. If your trying to make something home made try finding some acrylic tubing, that's what they make bongs out of. Look in the phonebook under plastics. If you have a TAP near you they should have it. Or, find a big piece of bamboo and use that. Anything but the PVC.