What is a gravity bong?
In “cannabis culture,” gravity bong is a term that can refer to either of two devices used for smoking cannabis that use water to create a vacuum whereby the suction created draws air through a bowl to fill the container with smoke. Gravity bongs differ from regular bongs in the fact that they usually do not filter the smoke through water, they have a far larger chamber, the smoke is much denser than possible in a standard bong, and they are usually homemade. Additionally, rather than the operator reducing the air pressure inside the device through inhalation, this is achieved with either falling water or by lifting the device itself while it is partially submerged in a bath of water. http://en.wikipedia.
