A gravity bong is a method of consuming smokable substances such as cannabis. The term describes both a bucket bong and a waterfall bong, since both use air pressure and water to develop smoke.
The bucket bong is made out of two containers, with the larger, open top container filled with water. The smaller has an attached bowl and open bottom, and the smaller is placed into the larger. Once the bowl is lit, the operator must move the small container up, causing a pressure difference. Smoke slowly fills the small jar until the user removes the bowl and inhales the contents. A waterfall bong is made up of only one container. The container must have a bowl and a small hole near the base so the water can drain easily. As the water flows out of the container, air is forced through the bowl and causes the substance to burn and accumulate smoke in the bong.
The construction of a bucket bong (or simply a "bucket") calls for a large plastic bottle (about 2 litres (0.53 US gal)), a large bucket or other container that both the bottle and a large amount of water will properly go into, a brass cut nozzle used as the bowl, an aerator screen cut to fit the bowl, and a large bucket or container. The large plastic bottle's base is cut off, and the bottle's cap has a small hole in the center which will eventually hold a bowl. The screen is placed inside of the bowl. The cut nozzle is threaded into the hole outside the cap.
The cap is then packed with a smokable substance, and screwed onto the bottle once it is immersed to its neck in liquid. While lighting the bowl with (preferably) a lighter or match, the bottle is gradually lifted until it is about to come out of the water or when the substance discontinues burning. While the bottle is held in place, the lid is removed, the user's mouth is placed on the bottle opening, and the user inhales as the bottle is pushed back down into the water. The cause of the smoke being expelled by the bottle's movement is the rise in internal pressure, created when the water volume increases; the smoke enters the lungs in a "smoother" manner than inhaling from a joint, blunt, or bowl by itself. This will give the smoker a sudden dose with hardly any smoke lost, rather than the amount of smoke lost with joints and blunts.
Author Brian Griffin—who also wrote under a pseudonym—noted the aesthetic downside of a gravity bong to be that it looks like "something a janitor whipped up using items from his closet." Griffin also wrote that the bong is quite difficult to conceal, saying: "they can be hard to hide if civic-minded parents or parole officers plan on making visits." An author under the pseudonym Will B. High insisted that the bucket bong's existences was "indisputable evidence" that marijuana smokers were more intelligent and inventive than one might assume. I. M. Stoned, author of Weed: 420 Things You Didn't Know (or Remember) about Cannabis called the bucket bong "out of the world" and "killer sweet."
A waterfall bong (or reverse bucket bong) is another method of smoking. It is assembled using a large plastic bottle (preferably about 2 liter), a bung or rubber stopper, a brass cut nozzle to act as a bowl and keep the marijuana (or other herbs) from entering the bottle, and an aerator screen. Once the bottle is filled to its neck in water the lid is screwed on, removing the rubber stopper and igniting the contents of the bowl leads to draining water to cause smoke to be drawn into the bottle. The cap is removed after the water has completely drained out, allowing the user to inhale the smoke.
Comparison to other herbal consumption methods
The bong is typically used for smoking cannabis and is generally not recommended for smoking tobacco or other herbal substances. The bong is, however, often marketed for use of tobacco, especially where marijuana smoking is illegal  The pressure created by the action of inhaling smoke into the user's lungs is very low when using a waterfall, contrary to other smoking devices, as gravity fills the chamber with smoke, creating less work for the smoker's lungs. Because the gravity bong does not use water to filter the cannabis, it is different than water pipes and water bongs. Vaporizers do not produce smoke, but the inhalation process is similar. A joint can contain from 0.4 g to well over 1 g and blunts can contain up to 3 g of cannabis, while the bucket bong only uses about 0.1 g to 0.3 g.
Internationally, the sale of gravity bongs is often prohibited in countries where marijuana is illegal due to its association with the herb. In the United States, under the Federal Drug Paraphernalia Statute, which is part of the Controlled Substances Act, it is illegal to sell, transport through the mail, transport across state lines, import, or export drug paraphernalia, meaning that the bong is illegal. Since Colorado, Oregon, and Washington have legalized recreational use of the herb, gravity bongs (along with other related paraphernalia) can be legally sold to anyone over the age of 21. In countries and states where use of cannabis is illegal, some retailers insist that bongs are intended for use with tobacco in an attempt to circumvent laws against selling drug paraphernalia. While technically the term "bong" does not mean a device used for smoking mainly marijuana, drug-related connotations have been formed with the word itself (partly due to punning with Sanskrit bhangah, meaning "hemp"). Thus for fear of the law some head shops will not serve customers who use the word "bong" or "bongs", typically insisting instead on the term "water pipe".
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