I've got an all-glass bong, I can post a pic this weekend to show you all...basically it has a shotgun, but the bowl/stem slide out for the filling and the cleaning. where the slide meets the body of the bong is all glass, and as near as I can tell its airtight...not really sure how, but I noticed that theres aboot an inch of length where the two peices are in contact, and the surface of the glass there is not smooth like the rest of the bong, it feels like super-high-grain sandpaper instead.

another version I've seen is my friends bong, standards shape and such, all glass. the slide bowl is glass, the receptacle for it is glass, but between the receptacle and the bong body is a rubber grommet...and it smokes fantastically as well, never tasted rubber with it yet