Shortened name for a Gravitational (Gravity) Bong, a smoking device consisting of a larger,
open container (Think - a bucket) and a smaller (Think -
2 liter soda bottle). The Larger base container is filled with water, and a whole(s) are drilled into the bottom of the 2 liter bottle, and a cap (Commonly called a 'grav
cap') Which can be made out of a ratchet or tin foil and the cap to the two liter bottle to filter the goods, which lets the smoke fill the chamber of the 2 liter bottle as you pull it upwards out of the water.