i think gravity bongs are fucking retarded, and are only useful if you have a huge amount of shitty weed sitting around that you have to burn up quickly, for whatever reason. they end up burning lots of the plant matter without vaporizing the THC, and you don't get all the THC you can out of the bowl... or at least, not as much as you could get out of a bowl/joint. it's that suction created by pullling the damn bottle out of the water... it creates way too high a temp. in the bowl for propa weed smokin', in my opinion. i've sworn them off and refuse to pack em