... actually vaporizing is the cleanest way. Bongs are actually conterproductive.

http://www.maps.org/mmj/vaporizer.html

There is all kinds of stuff in there about how clean vaporizer hits are and how dirty everything else is. Again, no conclusive study has ever been done to PROVE that there isn't a link between weed and cancer. Simply because there have been no reported cases of weed leading to cancer doesn't mean they never happened.