allowing clean air to circulate and clear the smoke chamber, ensuring no smoke dissipates without being properly consumed. Types of bongs: Classical bongs. Gravity bong (also known as a grav, bucket, bucky (in New Zealand), submarine, geeb, or GB) is a hydropneumatic device used for smoking cannabis. A typical variant consists of a bucket of water in which is typically placed a bottle with the bottom cut off, such as a 2-litre PET soft drink bottle. However, commercial gravity bongs made of boroslilicate glass exist too. Some kind of cap or screen is rigged over the mouth of the bottle and filled with hash or cannabis. A flame is then held near enough to heat the drug while the bottle is slowly raised out of the water, creating a negative gauge pressure inside the bottle, drawing smoke from the heated cannabis—along with air—into the vacuum. The cap or screen is removed once the bottle is almost full, the user's mouth is placed over the mouth of the bottle and the bottle pushed back down into the water, causing the pressure to rise and forcing the smoke into the lungs. There are many variants on this basic premise, such as using a large water cooler tank in lieu of a soft drink bottle. Waterfall bong: Similar to a gravity bong, a waterfall bong utilizes both a bottle and a cap or screen rigged over the bottle's mouth to hold cannabis. In this case, however, the bottle—which has one or several holes drilled near or at the bottom—is either filled with water or placed in a larger container filled with water before the cannabis is packed. The holes are then uncovered, or the bottle is simply raised from the container, evacuating the water either onto the ground or back into the container. When heat is applied to the drug, the resultant smoke is forced into the bottle with negative gauge pressure, as with the gravity bong. Once the water is evacuated, the smoke can be inhaled from the bottle. Variations on this concept are also used. Commercial gravity bongs made of boroslilicate glass exist too. Spots Spotting refers to a method of smoking cannabis. In this method, small pieces of cannabis are rolled (or simply torn from a larger bud) to form the "spot". Generally, the tips of two knife blades are heated, the spot is compressed between the two blades, and