Toilet
Flush toilet

A typical flush toilet is a ceramic bowl (pan) connected on the "up" side to a cistern (tank) that enables rapid filling with water, and on the "down" side to a drain pipe that removes the effluent. When a toilet is flushed, the sewage should flow into a septic tank or into a system connected to a sewage treatment plant. However, in many developing countries, this treatment step does not take place.

The water in the toilet bowl is connected to a pipe shaped like an upside-down U. One side of the U channel is arranged as a siphon tube longer than the water in the bowl is high. The siphon tube connects to the drain. The bottom of the drain pipe limits the height of the water in the bowl before it flows down the drain. The water in the bowl acts as a barrier to sewer gas entering the building. Sewer gas escapes through a vent pipe attached to the sewer line.

The amount of water used by conventional flush toilets usually makes up a significant portion of personal daily water usage. However, modern low flush toilet designs allow the use of much less water per flush. Dual flush toilets allow the user to select between a flush for urine or feces, saving a significant amount of water over conventional units. One type of dual flush system allows the flush handle to be pushed up for one kind of flush and down for the other, whereas another design is to have two buttons, one for urination and the other for defecation. In some places, users are encouraged not to flush after urination. Flushing toilets can be plumbed to use greywater (water that was previously used for washing dishes, laundry, and bathing) rather than potable water (drinking water). Some modern toilets pressurize the water in the tank, which initiates flushing action with less water usage.

Another variant is the pour-flush toilet. This type of flush toilet has no cistern but is flushed manually with a few liters of a small bucket. The flushing can use as little as 2–3 litres (0.44–0.66 imp gal; 0.53–0.79 US gal). This type of toilet is common in many Asian countries. The toilet can be connected to one or two pits, in which case it is called a "pour flush pit latrine" or a "twin pit pour flush to pit latrine". It can also be connected to a septic tank.

Flush toilets on ships are typically flushed with seawater.
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