Gravity bongs (also known as a grav, GB, ghetto bongs, bucket bongs, or waterfall bongs) are a special type of cannabis smoking pipe that use air pressure and water to draw smoke.
The pressure between the empty water bottle and the water in the bucket funnels smoke up through the bowl or socket. In a standard gravity bong, you light the bowl as you draw the bottle out of the water. This creates a suctioned force by gravity and pulls dense and potent smoke through.
Instead of taking multiple hits like you do from a traditional bong, you can actually smoke an entire bowl (or maybe even two to three) in a single hit from a gravity bong. This fast and powerful high is for experienced users, not beginners!