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Close coupled cistern type flushing toilet.

A flush toilet or water closet (WC) is a toilet that disposes of the waste by using water to flush it through a drainpipe to another location. Modern toilets incorporate an 'S' bend; this 'trap' creates a water seal which remains filled with water between flushing, thus providing a hygienic barrier by preventing sewer gases from passing up the drainpipe. During flushing the 'S' bend also provides siphon action which helps accelerate the flushing process. Water filling up the bowl creates a high pressure area which forces the water past the S bend. At the S bend when water starts to move it creates a vacuum that pulls the water and waste out of the toilet. When no more water is left then the air stops the siphon or vacuum process. At that point the water that is going into the bowl continues to fill up the bowl to equalize the bowl and the S bend. This ends the cycle of one flush. However, since this type of toilet does not generally handle waste on site, separate waste treatment systems must be built.

Further information: History of toilets

Toilet with elevated cistern and chain attached to lever of discharge valve.

As with many inventions, the flush toilet did not suddenly spring into existence, but was the result of a long chain of minor improvements. Therefore, instead of a single name and date, there follows a list of significant contributors to the history of the device.

• circa 30th century BC: A primitive dual channel, fresh water and waste, toilet system was in use in the houses at Skara Brae, Orkney, Scotland
• circa 26th century BC: Flush toilets were first used in the Indus Valley Civilization. The cities of Harappa and Mohenjo-daro had a flush toilet in almost every house, attached to a sophisticated sewage system.^{[citation needed]}
• circa 15th century BC: Flush toilets were found in the remains of the Minoan city of Akrotiri.
• Roman Empire: Some examples include those at Vindolanda on Hadrian's Wall in Britain. With the fall of the Roman Empire, the technology was lost in the West.
• 1596: Sir John Harington is said to have invented 'The Ajax', a flush toilet, for Elizabeth I of England, who wouldn't use the contraption because it made too much noise. His design was ridiculed in England, but was adopted in France under the name Angrez. The design had a flush valve to let water out of the tank, and a wash-down design to empty the bowl.
• 1738: a valve-type flush toilet was invented by JF Brondel.
• 1775: Alexander Cummings invented the S-trap (British patent no. 814?), still used today, that used standing water to seal the outlet of the bowl, preventing the escape of foul air from the sewer. His design had a sliding valve in the bowl outlet above the trap.
• 1777: Samuel Prosser invented and patented the 'plunger closet'.
• 1778: Joseph Bramah invented a hinged valve or 'crank valve' that sealed the bottom of the bowl, and a float valve system for the flush tank. His design was used mainly on boats.
• 1819: Albert Giblin received British patent 4990 for the "Silent Valveless Water Waste Preventer", a siphon discharge system.
• 1852: J. G. Jennings invented a wash-out design with a shallow pan emptying into an S-trap.
• 1857: the first American patent for a toilet, the 'plunger closet', was granted.
• 1860: The first watercloset was installed on the European continent and was imported from England. It has been installed in the rooms of Queen Victoria in castle Ehrenburg (Coburg, Germany) and she was the only one who was allowed to use it.
• The first popularized water closets were exhibited at Crystal Palace and they became the first public toilets, they had attendants dressed in white and they charged only a penny coining the term "To spend a penny"
• 1880s: Thomas Crapper's plumbing company built flush toilets of Giblin's design. After the company received a royal warrant, Crapper's name became synonymous with flush toilets. Although he was not the original inventor, Crapper popularized the siphon system for emptying the tank, replacing the earlier floating valve system which was prone to leaks. Some of Crapper's designs were made by Thomas Twyford. The similarity between Crapper's name and the much older word crap is merely a coincidence.
• 1885: Thomas Twyford built the first one-piece china toilet using the flush-out siphon design by J. G. Jennings.
• 1886: an early jet flush toilet was manufactured by the Beaufort Works in Chelsea, England.
• 1906: William Elvis Sloan invents the Flushometer, which uses pressurized water directly from the supply line for faster recycle time between flushes. The original Royal Flushometer is still in use today in public restrooms worldwide.
• 1980: Bruce Thompson, working for Caroma in Australia, developed the Duoset cistern with two buttons and two flush volumes as a water-saving measure. Modern versions of the Duoset are now available in more than 30 countries worldwide, and save the average household 67% of their normal water usage.^[1]

The bowl, or pan, of a WC is the receptacle into which body waste is excreted; the pan is usually made of vitreous china, but sometimes made of stainless steel or composite plastics. WC bowls may be pedestal (free-standing), cantilever (wall-hung), or squat in design. There are several types of pans in common use: washdown, washout, and siphon. In less common use is the valve closet. There are "male" and "female" bowls also. Males prefer the larger, elongated (or oval) bowls for "penis clearance" while sitting for defecation while females often prefer the smaller, rounder bowls. A toilet in a household bathroom used chiefly or solely by women in America is apt to have a smaller, rounder bowl. The outer edge of a toilet bowl is termed the "rim".

Washdown WCs are the simplest in design. They take the form of a 'funnel' shape, with a broad opening at the top narrowing to a smaller outlet connected to a drain. The pan usually incorporates a water trap at the base to seal the open end of the pan from the sewer.

Washdown pans have almost vertical surfaces at the back of the pan and more gently sloping fronts to allow the outlet of the pan to be directly beneath the anus of a seated user to prevent soiling of the bowl.

Washout pans have a shallow pool of water into which waste is excreted. Waste is cleared from the pan by being swept over a weir and into a drain by water from the flush. Washout pans are popular in several countries in Europe, notably Germany and The Netherlands.

The bowl of a flush toilet is a porcelain vessel; in North America and Great Britain this often has a built-in siphon, usually visible as a curved pipe protruding from the back (the "S-bend"). Normally, the bowl contains a small amount of water which is enough to form an air trap inside the siphon pipe, preventing foul air escaping from the sewer. When the toilet is used, liquid flows slowly through the siphon pipe as waste matter is added, but the flow volume is too small to fill the siphon. To flush the toilet, the user activates a flushing mechanism (see below) which pours a large quantity of water quickly into the bowl. This creates a flow large enough to fill the siphon tube, causing the bowl to empty rapidly due to the weight of liquid in the tube. The flow stops when the liquid level in the bowl drops below the first bend of the siphon, allowing air to enter which breaks the column of liquid.

The earliest type of WC, the valve closet is now scarce. More complicated in design than other water closets, reliability is lower and maintenance more difficult. The most common use for valve closets is now in portable closets for caravans and camping.

The valve closet has a valve or flap at the exit of the bowl with a water-tight seal to retain a pool of water in the pan. When the WC is flushed, the valve is opened and the water in the pan flows rapidly out of the bowl into the drains, carrying the waste with it.

In Germany and elsewhere in Europe it is not uncommon for the toilet bowl to allow feces to rest on a ledge before being washed away by the flush. The design of many German lavatory bowls is the reverse of that in most other western countries, with the sewer outlet towards the front of the bowl rather than at the rear.

For a review of Japanese toilet usage and history, see Toilets in Japan.

• Cover

This short section requires expansion.

Retrofit direct flush installation in which the flushometer has been replaced with a sensor-operated system that automatically flushes the fixture when a user departs. The system uses an infrared proximity sensor to detect a user approaching the fixture, then it waits until the user departs. A solenoid is used to actuate the flush from a 6 volt battery inside the unit that also powers the sensor circuit.

The bowl siphon described above is triggered by a large flow of water into the bowl, which is provided by the flushing mechanism. This is usually of one of the following designs:

In the old-style manual flush systems, the user presses a button, which opens a flush valve allowing mains-pressure water to flow into the bowl, or sometimes the user presses directly on a flush lever (a handle connected directly to a flushometer). The valve contains a pneumatic mechanism that closes it after a preset time. This system requires no storage tank, but requires high volume water for a very brief time period. Thus a 3/4 inch (19 mm) pipe at minimum, and preferably a 1 inch (25 mm) pipe, must be used, but the high volume is used only for a short duration so very little water is used for the amount of flushing efficacy delivered. Direct valves are regulated by a device called a "flushometer" that meters out a certain controlled amount of water per flush. Direct flush makes the most efficient use of water, because it uses the water at full pressure and volume. The ability of water to perform the work in removing waste matter from the toilet bowl is given by pressure times volume. Typical pressure in an urban commercial building where flushometers are usually used is around 60 pounds per square inch (400 kPa) which is enough pressure to raise the water 137 feet (42 m) above the toilet bowl. Thus, in some sense, the effectiveness of direct flush is like having the tank 137 feet (42 m) above the bowl (lots of "flush energy").

Flush valves are not permitted on fixed WCs in Britain, although they are sometimes used in railway carriages.

A storage tank, or cistern, collects between 6 and 17 litres of water over a period of time. This system is suitable for locations plumbed with smaller diameter pipes. The storage tank is kept full by a float valve or ball cock. An outlet in the bottom of the tank is covered by a buoyant plastic cover (the flush valve) which is held in place by water pressure. To flush the toilet, the user pushes a lever, which lifts the flush valve from the outlet. The valve then floats clear of the outlet, allowing the tank to empty quickly into the bowl. As the water level drops, the floating flush valve descends back to the bottom of the tank and covers the outlet pipe again. This system is common in homes in the USA. Tank type toilets waste the energy in the water by converting the potential energy of 137 feet (42 m) (the "head" of pressure in typical North American city water mains) times acceleration due to gravity, into around 18 inches (460 mm) above the bowl. Some older style toilets mitigate this waste of energy to some degree by having the tank be as high as possible (up near the bathroom ceiling), but modern tank-type toilets waste the energy in the water, and therefore either use more water than necessary for a given flushing job, or for the same amount of water, flush less effectively than direct flush.

In the United States, 13L-per-flush toilets (still commonplace in Canada) have been banned in favor of 6L toilets. While conservation of water is an admirable goal, even the best 6L close-coupled (tank mounted directly on the bowl) toilets have a tendency to either become clogged themselves, or have the drain pipes beyond them become clogged due to insufficient velocity of the waste matter^{[citation needed]}.

Many manufacturers speak of "grams of tofu" and other "ratings"; it must be noted, however, that the toilet manufacturers have no vested interest in discussing the inevitable clogging further down the plumbing system. For optimum conservation of water, systems other than close-coupled tank-type toilets are preferable.

The flush valve is responsible for quickly emptying the tank (cistern) and driving the waste from the bowl.

In 1958 (citation: patent date), American Standard introduced a unique flush valve which differed from the conventional "flapper". Though no longer used in new toilets, this valve design remains an extremely popular upgrade when repairing an existing toilet.

The American Standard timed cup flush valve incorporates two cylinders mounted orthogonally, attached to a flushing disk.

Operation is best understood as follows:

1. Prior to flushing, the tank (cistern) is full of water. Both cylinders are submerged, and the flushing disk remains tightly shut due to the weight of the water pushing it against its seat.
2. With a flush, the disk is pulled away from the seat. Water escapes to the bowl. The horizontal cylinder provides buoyancy to hold the disk away from the valve seat. The vertical cylinder remains full of water.
3. As the tank empties, the buoyancy of the horizontal cylinder is compromised, but the vertical cylinder remains full of water which provides sufficient counterbalance to the flushing disk, holding it open.
4. After the tank has emptied, the water in the vertical cylinder drains through a 3/16" hole in the bottom of the cylinder. At some point after the tank has emptied, the mass of the flushing disk and horizontal cylinder exceeds the mass of the vertical (timing cup) cylinder, causing the flushing disk to fall back onto its seat.
5. The fill valve refills the tank for the next flush cycle.

A stellar benefit of the American Standard Timed Cup flush valve is that an incomplete flush is virtually impossible. Repairs are easy, generally requiring only a flushing disk.

The fill valve is responsible for refilling the tank (cistern) with water.

Toilets manufactured prior to 1990 are likely to include a "Hoover-style" ballcock, which is a fill valve employing a ball-type float mounted on an arm. As the float rises, so does the arm. The arm is connected to a linkage which blocks the water flow into the toilet tank, and thus maintains a stable level in the tank.

A one-piece fill valve consists of a tower which is encircled by a plastic float assembly. Operation is otherwise the same as a conventional Hoover ballcock, though the geometry is different. By virtue of the more compact layout, interference between the float and other obstacles (tank insulation, flush valve) is greatly minimized, thus reducing reliability issues (stuck floats, etc).

Many modern toilets use a Fluidmaster brand fill valve (ref. open any new high-end Kohler or American Standard toilet, look for the Fluidmaster name on the float); cheaper brands and models tend to use a similar concept replica.

The one-piece fill valve offers several advantages:
- Close-positioned float is less likely to become entangled in obstacles
- Close-positioned float will work in the vast majority of toilet tanks
- Design of valve assembly affords itself to quiet fills and shut-offs (no loud noises as the toilet refills)
- Geometry of valve and float design adapts well to anti-leak latching mechanisms, potentially saving the owner hundreds of dollars refilling a leaky toilet tank (http://www.fluidmaster.com/fill_products_400ls.html)

This system, invented by Albert Giblin and common in the UK, uses a storage tank similar to that used in the flush valve system above. The user pushes a lever or button, forcing the water up into a siphon (not to be confused with the bowl siphon, "S-bend") which empties the entire tank into the bowl. The advantage of a siphon over the flush valve is that is has no sealing washers that can wear out and cause leaks, so it is favoured in places where there is a need to conserve water. Until recently, the use of siphon-type cisterns was mandatory in the UK to avoid the potential waste of water by millions of leaking toilets.

Older installations used a high-level cistern, or high suite, fitted above head height, that was operated by pulling a chain hanging down from a lever attached to the cistern. Some people still refer to the act of flushing a toilet (even a new low-cistern, or low suite, type) as "pulling the chain" or "flushing the chain". Modern versions have a neater-looking low-level cistern with a lever that the user can reach directly, or a 'close-coupled' cistern that is even lower down and integrated with the bowl. This lower level results in loss of potential energy in the water, as the potential energy of water pressure is converted to the potential energy of height in a less advantageous manner, due to very little height, as described above. Consequently modern toilets usually do not flush as effectively.^{[citation needed]}

Not uncommon in the United States, this system (invented by R. Bruce Martin) uses the water pressure within a structure to compress air within a closed vessel located within the vitreous enclosure. When flushed, the compressed air pushes into the bowl at a velocity (flow rate in gallons per minute or liters per second) significantly higher than gravity flow. This system is more water efficient than a tank type and can be installed into the same fittings as the latter. It also costs 10% less than the new 3" (75 mm) gravity flapper equipped tank-type toilets. Pressure assist toilets are used in both private (single and multiple and lodging) bathrooms as well as light commercial installations (offices, etc.) They hardly ever clog and so require less maintenance, but tend to be noisier - a concern for residential settings.

"Automatic flush" refers to a triggering mechanism, rather than a water propulsion mechanism, although is usually implemented together with direct flush systems. Autoflush systems, as the name suggests, flush automatically once the user has left. Typically, an override button is provided if the user wishes to trigger flushing earlier or, when the system has true mechanical manual override, it can be pushed if the power source to the flush valve has failed. In retrofit installations, a self-contained battery-powered or hardwired unit can be added to an existing manual flushometer, which can automatically flush when a user departs.

There are two main kinds of machine vision systems used for sensor operated flush: passive and active. Passive systems such as passive infrared (PIR) see the body of the user by electromagnetic energy that is received by the sensor. Active vision systems provide a source of electromagnetic energy (radar, infrared, or the like) and see reflected energy from the target (the user of the fixture). Although units usually ship with a factory-set sensor range, installers can adjust the setting to accommodate special needs or circumstances, such as for restrooms primarily used by children.

Automatic flushing cisterns may also be of the siphonic pattern, where a siphon is activated once water fills the tank and begins to run through the siphon tube; this is the most common form of automatic operation in the UK.

If the flush mechanism should fail in any of these systems, the bowl siphon can be activated by emptying a large bucket of water into the bowl. A domestic hose pipe will not work, as it cannot supply water fast enough to fill the siphon tube. A larger hose, or small firehose, even a 3/4 inch (2 cm) garden hose thread (GHT) firehose, provides sufficient water to flush without a bucket.

For North American Valve Tank type toilets, if the handle should have be held down to achieve a complete flush an adjustment might need to be made in the handle-float-stopper mechanism. The handle of a toilet is typically attached to a stopper via a chain. A float is attached to the chain between the handle lever and the stopper. The float acts as a counter-balance to allow a certain amount of water to escape through the flush hole in the tank. The float mechanism on the chain should be some distance under the water level of the tank so it can keep the stopper open during a flush until the tank level reaches a certain level. At a certain level the float will pop to the top of the water and the stopper will close. The float should be at a position on the chain where it is under water and does not have so much buoyancy to allow water to leak through the stopper.

For British toilets, the siphon's hidden, oblong, plastic diaphragm will tend to split after around 10 years. The effectiveness of the flush can deteriorate suddenly or gradually as the number and size of splits increase. This will often prompt owners to replace much of the system. However, the diaphragms are of a standard design and are cheap (50p) and simple to replace. Inside the cistern, unhooking the flush-handle's s-link allows the plunger and diaphragm to be removed, once the lower part of the siphon is unscrewed (it is not necessary to remove the whole assembly -- the main outlet pipe can be left in place. There is also a small rubber diaphragm in the ballcock inlet assembly, which can deteriorate over a period of around 10 years -- if adjusting the water level becomes problematic, it is worth changing this inexpensive item (50p).

Flushometer type toilets are much more common in commercial installations (at least in the US); they're almost never seen in residential installations, except for dormitory and barracks areas. The installation of large numbers of toilets in buildings like sports stadiums has led to a test which is commonly performed before the final release of such a project, which is called "The Flush". It entails stationing individuals in each restroom in the facility -- in large installations this can amount to 100-400 people -- and cueing them all by radio to flush their toilets as close to simultaneously as possible.

The purpose of the test is twofold: it checks that the plumbing design engineers got their sums right on the sizes of both the main water supply to the building, and also the size of the drain piping. The test is commonly not made public before it happens, so as to avoid embarrassment in the event of a failure.

Frequently, in public restrooms in the United States and other countries, as a courtesy to others using the restroom, toilet users may perform what is as known as a "courtesy flush," where the user flushes after the initial release of feces to minimize the odor. Since it is not so much the feces as the accompanying flatulence that causes much of the odor, performing a flush soon enough after the intial release causes the odor to be sucked away removing much of it before it spreads to adjacent areas.^{[citation needed]} Subsequent release of feces in the same session does not usually produce as much flatulence so additional courtesy flushes are not required (user's discretion).

A similar technique is often used with modern, less-efficient "low cistern" designs and "water efficient" system, to reduce the likelihood that the toilet will block or fail to clear completely on the final flush. Whether this technique wastes more water than older designs, or the additional flushing required to clear a blocked or incompletely flushed toilet is debatable.

The water closet was the original term for a room with a toilet, since the bathroom was where one was to take a bath. This term is still used today in some places, but might be a room that has both toilet and bath. Plumbing manufacturers often use the term to delineate toilets from urinals.

1. ^ 100 Years of Australian Innovation - Dual flush technology

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• Intelligent Bathroom Fixtures and Systems (comparison between passive and active vision systems for use with plumbing fixtures, as published in Leonardo, 36(3), pp 199–120, June 2003)
• A Brief history of Wells and Toilets, 2005 book (link to pdf-file)
• Did Thomas Crapper invent the flush toilet? - at Snopes
• "Superflushing their way to the Super Bowl" - PM Engineer
• Toilet, its history and reality.