CAUTION: 
REMAIN SEATED WHILE SMOKING OUT OF A GRAVITY BONG. IF DONE PROPERLY IT WILL MAKE YOUR HEAD RUSH AND YOU DON'T WANT TO FALL AND HURT YOURSELF! 1. Get a round 1/2 gallon pitcher. The pitcher should be a little bigger in diameter than the coke bottle.
2. Get a 2 liter plastic coke bottle. The coke bottle should be a little taller than the pitcher. This will prevent your weed from getting wet.
3. In the US, we can buy an aluminum pipe with a screw top and a rubber mouth piece that fits perfectly in the mouth of the coke bottle, otherwise use a piece of aluminum foil in the top with some very small holes punched in it like a screen.
4. Cut the bottom off the 2 liter bottle.
5. Fill the pitcher 80% full with water.
6. Take the cap off the coke bottle and place it in the pitcher.
7. Place the pipe or foil and weed into the top of the coke bottle.
8. While lighting the weed, slowly pull the bottle out of the pitcher. This will fill up the bottle with smoke like your lungs.
9. Carefully lift out the pipe/foil (don't burn yourself).
AND ABOVE ALL DON'T LET ALL THE SMOKE ESCAPE BEFORE THE NEXT STEP 10. Place your mouth over the bottle mouth and press slowly back into the pitcher. This will push the smoke out of the bottle and into your lungs.
12. Sit back relax and enjoy
