flamingweasel's write up gives a good account of how to make a gravity bong (aka "bucket" in the UK) out of two plastic bottles. However, when it comes to drug paraphernalia, diagrams are always useful in understanding how the device works. Apologies in advance for my ASCII art skills!
N.B. My design differs slightly in that it uses a nut (bowl) and downtube from a conventional bong, rather than the handmade bottle-top bowl flamingweasel uses.
Key:
####
#### = unburnt "mix" (i.e. roasted tobacco and cannabis)
$$$$
$$$$ = burning "mix" (i.e. you're holding a lighter under it)
~~~~ = water level
****
**** = smoke
| |
\ /
|| = "nut" (UK) or "bowl" (USA)
[= =]
[= =] = bottle top with hole in centre
|##|
\##/
||
[=||=] STARTING
[=||=] POSITION
| || | (top bottle-half is down)
/ || \
/ || \
/ \
/ \
/ \
/ \
/ \
| | | |
|~~|~~~~~~~~~~~~~~~~~~|~~|
| | | |
| | | |
| | | |
| |
\________________________/
| |
\$$/
||
[=||=] BURNING
[=||=] POSITION
|*||*| (top bottle-half pulled up)
/*||*\
/**||**\
/********\
/**********\
/************\
/**************\
/****************\
|******************|
|******************|
| |******************| |
|~~|~~~~~~~~~~~~~~~~~~|~~| <- N.B. water level will
| | | | take a second or two
| | to stabilise
| |
| |
\________________________/
**** <- smoke going into mouth
|****|
/****\ INHALING
/******\ POSITION
/********\ (cap unscrewed and top
/**********\ bottle-half pushed down)
/ \
/ \
/ \
| | | |
|~~|~~~~~~~~~~~~~~~~~~|~~|
| | | |
| | | |
| | | |
| |
\________________________/