Flush toilet

A flush toilet, also known as a water closet (WC), is a plumbing fixture used to dispose of human waste. It works by collecting urine and feces in a bowl and using water to channel them through a drainpipe. This waste is then sent to a treatment facility or a local system like a septic tank. These devices are essential for modern sanitation and public health. Most residential models are made of porcelain or vitreous china. However, public or institutional toilets are sometimes constructed from metal or other durable materials.

To prevent odors, flush toilets incorporate a specific plumbing component called a trap. This is a bend in the pipe, shaped like an S, U, J, or P. The trap causes water to collect in the bowl, creating a liquid seal. This seal is vital because it blocks noxious sewer gases from entering the building. When a user triggers a flush, the rapid flow of water rinses the entire internal surface of the bowl. This is achieved through a molded flushing rim or specialized jets around the top of the bowl.

Most household toilets use a cistern, which is a fixed tank located above or behind the bowl. The cistern holds a specific volume of water and contains two main devices. The first device releases water rapidly into the bowl to sweep waste into the drain. The second device is a fill valve that automatically replenishes the tank after each use. To control the water level, the fill valve uses a float. In a side-float design, a ball-shaped float sits on a lever arm. In a concentric-float design, which has been used since 1957, the float encircles a central tower. This newer design is more compact and can even signal a leak by making more noise.

There are different mechanical methods for discharging water from the cistern. One common method uses a flapper-flush valve, often found in North America and continental Europe. This system uses a buoyant plastic or rubber cover called a flapper. When the user presses a lever, the flapper lifts from its seat, allowing water to rush into the bowl. Once the tank is empty, the flapper descends to seal the outlet. Another method is the siphon-flush mechanism, which was invented by Albert Giblin. This system is common in the UK and is sometimes called a valveless system. It uses a vertical pipe and a domed chamber to create a siphonic flow that pulls water through the bowl.

Different environments require different flushing technologies. In urban and suburban areas, toilets connect to a sewerage system that leads to a sewage treatment plant. In rural areas, people often rely on septic tanks or composting systems. Some regions use a manual pour flush, which requires no permanent water supply. In these cases, a user pours a few liters of water from a container into the bowl. This method is common in many Asian countries and can connect to twin pits or a septic tank.

Specialized vehicles like trains, aircraft, buses, and ships often use vacuum toilets. These toilets connect to a vacuum sewer system that removes waste through suction. They are highly efficient, often using less than 0.5 liters of water per flush, or sometimes none at all. Some vacuum systems even use colored disinfectant instead of water. Using vacuum technology saves significant weight on vehicles and prevents water from sloshing out of the bowl during motion. These systems can also separate blackwater from greywater to help with biogas production.

In recent years, engineering has improved how toilets function. Ceramic engineers found that improving the waterway design is more effective than simply mounting tanks higher up. This led to the popularity of the close-coupled tank-bowl combination. Older "high suite" models used a high-level cistern with a pull chain, while "low suite" models placed the tank lower. Today, many modern toilets also feature dual flush options. These allow users to choose a lower water level for liquid waste and a higher level for solid waste, maximizing water savings.