gravity bong

1. Get two 2-liter bottles, a screen, a sharp knife, a bucket / largish water receptacle, some tape (electrical, duct, or masking is best), and a drilling impliment
2. Take the caps off of the bottles. Drill a decent-sized hole through the tops of the caps, put the tops together with the screen in between, and tape together. the result looks like a female-female connecter with a filter
3. With the knife, cut the bottom off of one of the bottles.
4. Screw the cap contraption into the bottle you just cut, and discard the shit that's lying around. Put away the knives and drilling impliments.
5. Put the material in the cap thing (notice how it's shaped like a bowl? cool, no?)
6. Slowly immerse the bottle in water. Not too fast, or you'll volcano the material
7. Light the material, then slowly draw the bottle up. The chamber of the bottle will fill with really thick smoke if you're doing it properly.
8. Keep the bottom of the bottle in the water; you don't want the smoke to escape.
9. Remove the cap, put your mouth over the top of the bottle, and push the bottle back down into the water. Remember to breathe in :)
10. And try not to fall backwards when you're done...

• One 600 ml pop bottle. (larger if you like, I suppose, this is big enough for me)
• Bowl assembly of some sort (I use one I bought from a local head shop)
• Knife, or any suitably sharp object

• Cut a small hole in the bottom of the bottle
• Cut a hole in the cap to put your bowl in
• Put your bowl in the cap-hole
• Fill bowl with your favorite cumbustable, plug the bottom-hole with your finger, fill the bottle with water, put the cap/bowl on, light, and release the water.
• enjoy

• One 2L bottle with cap
• One pitcher or similar Water Mass Storage Device (sinks and bathtubs are OK)
• One cheap-o Bic ballpoint pen with guts removed, or similar plastic cylinder
• One bowl assembly (see eyedropper suggestion)
• Water

• Cut the bottom from the 2L bottle
• Drill a hole through the bottle's cap - it should be a bit wider than the circumference of the bowl
• Seal one end of the pen to the underside of the bowl - I have always used rubber gaskets, but candle wax, scotch tape and the like are OK.
• Insert the pen/bowl through the hole in the bottlecap so the bowl is just above the surface of the cap and pointing upward
• Seal the pen/bowl to the bottlecap so it is airtight
• Screw the bottlecap/pen/bowl onto the 2L bottle
• Fill the pitcher with water
• Place the 2L bottle/bottlecap/pen/bowl upright in the pitcher, so that the water level comes to the neck of the bottle and the pen is sticking straight down into the water

• Pack the bowl with one hit's worth of marijuana.
• While holding a lighter over the bowl, raise the bottle assembly slowly and evenly out of the water.
• Gravity will pull the water down, creating a vacuum at the top of the bottle. Some air from outside the bottle will want to fill the vacuum.
• The lighter's flame is sucked down into the bowl, igniting the marijuana. The smoke is pulled down through the pen. Once it hits the water, it becomes encased in a bubble. The bubble rises to the surface of the water and pops (this looks neat).
• After the marijuana in the bowl has been reduced to ash, unscrew the cap/pen/bowl and remove. Take care not to drop the bottle back into the pitcher - try to hold it as steadily as possible.
• Place your mouth over the mouth of the bottle, and with one hand holding it against your lips, drop the bottle back into the pitcher.
• The smoke will shoot down your throat into your lungs.
• After a few minutes have passed, exhale.
• Repeat until you can't remember your name.

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)
      /            \
     /              \
    /                \
|  |                  |  |
|~~|~~~~~~~~~~~~~~~~~~|~~|
|  |                  |  |
|  |                  |  |
|  |                  |  |
|                        |
\________________________/