A homemade construction, often made from a water bottle or a toilet paper roll; the purpose for a b-tube is to exchange the smell of marijuanna for that of fabric softner. A b-tube is made of a tube with pieces of fabric softner inside. The word b-tube has derrived from 'bounce tube,' refereing to Bounce, a fabric softner company.
Edgar: Yo esse, it's starting to reek in here
Chale: No problem holmes, we'll just start using the b tube
Harry: Yo man, do you have an fabric softner?
Tom: Yeah, why do you need it?
Harry: oh, no biggie, i'm just blazing in my room, and i dont want it to smell too much.