bathtub bong

The item of marijuana paraphernalia that is evolved when one is so chronic that one brings ones gravity bong into the bath with oneself.

Usually in the form of a 2-liter soda bottle with the bottom cut off, the bathtub bong is always the piece in a marijuana smoker's collection that he has had the most fond memories with.

Because you can't call yourself a pothead if you haven't passed out in a bath full of warm bong water.

Stoner: "Yo, Brosephus Rex, where's my bathtub bong?"
Roommate of Said Stoner: "I was using it in the sink like a normal person, you fuckin' pothead."