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Modern low-flush toilet

Flush toilets

by Chris Woodford. Last updated: December 11, 2013.

Toilet, lavatory, loo, water closet, WC, John, crapper, can—it's amazing we have so many names for something we care to talk about so little. Toilets are hardly the most glamorous of inventions, but imagine trying to live without them. About 40 percent of the world's people (some 2.6 billion of us) are in that unhappy position, lacking even basic sanitation. At the opposite end of the scale, in Japan, people have amazing electronic toilets that do everything from opening and closing the lid automatically to playing music while you use them. Most of the world's toilets are more modest than this, but they're still pretty ingenious "machines." Let's take a closer look!

Photo: Like most new toilets, this low-flush model is designed to save water; the two buttons on top let you choose whether to flush with a large or a small amount. Exactly how much difference that will make to your water consumption varies from one household to another. An old-style flush toilet typically uses 13 liters (3.4 US gallons), where a low-flush model will use only 6 liters (1.6 US gallons) and some models use only 4.8 liters (1.3 US gallons). If you save 7 liters (1.8 US gallons) per flush and people in your home flush 10 times a day, you'll save at least 25,500 liters (6700 US gallons) per year. You'll save more or less depending on how many people there are in your household.

Flush and go

Flush mechanism inside the cistern of a toilet

At first sight, toilets seem quite simple: you have a waste pipe going through the floor and a tank of water up above (called a cistern) waiting to flush into it when someone pushes a button or pulls a lever or a chain. Most flush toilets are purely mechanical: pull the chain and the cistern empties through the force of gravity, washing the bowl clean for use again. They are literally mechanical because they flush and refill using levers inside—and levers are examples of what scientists call simple machines.

There's a little bit more to toilets than this. When you flush, the cistern has to refill automatically from a kind of faucet on the side and the refilling operation has to last just long enough to fill the tank without making it overflow. The "hole in the ground" is more sophisticated than it looks as well. You may have noticed that toilets always have a little water in the bottom of them; even when you flush them, they never empty completely. Some water is always trapped in a big curved pipe at the base of the toilet known as the S-bend (or S-trap). This little bit of water effectively seals off the sewage pipe beneath it, stopping germs and bad smells from coming up into your bathroom.

Photo: Lift the cistern on a toilet and this is what you'll find inside. The cistern (upper tank of water) drains through a valve in the center through the force of gravity. The blue, balloon-like object on the left is a plastic float that drops when the water level falls. This tilts the plastic lever (known as the ballcock) and allows the cistern to refill.

What happens when you flush?

Animation showing the different parts of a toilet and how they work during a flush

  1. Press the handle to flush the toilet and you operate a lever inside the cistern.
  2. The lever opens a valve called the flapper that allows the cistern to empty into the toilet bowl beneath.
  3. Water flows from the cistern through holes in the rim so it washes the bowl as well as flushing the contents away.
  4. There's enough water flowing down from the cistern to flush the toilet around the S-bend (S-trap). Some water always remains at the bottom of the toilet, however, for hygiene reasons.
  5. The contents of the toilet are flushed down the main drain.
  6. As the cistern empties, the plastic float falls downward, tilting the ballcock lever.
  7. The ballcock opens the inlet valve at the base of the cistern, which works a bit like a faucet (tap). Water flows in, refilling the cistern, and pushing the float back up again. When the float reaches the correct level, the ballcock switches off the water supply and the toilet is ready to flush again.

Who invented the flush toilet?

Although it's popularly believed that flush toilets were invented by an English plumber called Thomas Crapper (c.1836–1910), it's an unhelpful myth, for two reasons: flushing toilets are an ancient technology and no single person can really claim to have invented them: dozens (if not hundreds) of different inventors have been involved in their development over the years, especially since Crapper's lifetime. Archaeological evidence shows that primitive toilets using river water to flush wash away waste are over 5000 years old and date back to something like 3000BCE. The two inventors who have the best claim to our modern toilet-flushing system were born hundreds of years before Crapper. Among his many other achievements, prolific Arabic inventor and engineer Al-Jazari developed a flushing hand-washing device in 1206, while English writer and courtier Sir John Harington (1561–1612) described a method for flushing a toilet in 1596 in his article A New Discourse of a Stale Subject, Called the Metamorphosis of Ajax.

Search through the invention records at the US Patent and Trademark Office and you'll find literally hundreds that relate to toilets and their flushing mechanisms. I've chosen two examples from 1874 to give you a flavor of what you can find. On the left (and drawn in plan view, from above), we have the self-disinfecting water-closet basin developed by Jabez Burns, Charles Higgins, and William Higgins ("Improvement in Water-Closet Basins", US Patent#149,195). Their simple innovation was to make the pipe that fills the toilet basin squirt sideways over a bar of soap, thus disinfecting the basin and stopping any smell. On the right, you can see Archibald McGilchrist's trap-less water closet ("Improvement in Water-Closet Apparatus", US Patent#157,211). Unlike with an S-bend closet, there is no water trap to stop odors. Instead, the flush mechanism raises and lowers a ball-shaped valve that seals the waste pipe. A rising and falling float (I've colored it green in the artwork) operates a valve mechanism (colored yellow) to refill the basin in the usual way. You can explore lots more similar inventions with a search for "water closet" on Google Patents (it just gave me 13,000 results!).

Water closet with built-in disinfectant dispenser Water closet with trapless flush mechanism

Artwork: Two examples of 19th-century improvements in water closets (toilets) by American inventors.
Images courtesy of US Patent and Trademark Office with added coloring and annotations by Explainthatstuff.com.

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Text copyright © Chris Woodford 2008, 2012. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2008) Toilets. Retrieved from http://www.explainthatstuff.com/howtoiletswork.html. [Accessed (Insert date here)]

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