Gravitron manufactures all-glass gravity bongs that are as effective as a homemade one but are easily broken, not easily stored or transported, and considered legitimate paraphernalia. A bucket and a cut up bottle could easily be some silly science experiment a homemade musical instrument. Just hide the grav top :]
"Shit, I just pulled 4 gravs. I'm BLAZED"
"Let's go make a grav."
"Fuck it, let's not watch the Clippers, let's go home and do gravs and play Sega Genesis."
"Eww dude, you got resin on your teeth from that huge grav, gross."
"not much, Jan Oliver tried to eat me today but couldn't waddle to me fast enough."