Travel & Day Trips

How Do Airplane Toilets Work? The Science and History

Airplane toilets, though small and sometimes a little cramped, are marvels of engineering. They are specifically designed to work effectively at high altitudes.

In this blog post, we will delve into the fascinating world of airplane toilets and understand how they work.

The Evolution of Airplane Toilets

In the early days of aviation, the toilets on airplanes were very basic and not very different from regular toilets. Sometimes, they were as simple as a container and an open window! Not quite the luxurious image we usually associate with early aviation!

This delightful article shares some of the lavatory challenges of military aviators in the early days.

However, as airplanes began to fly higher and for longer durations, it became evident that a specialized toilet system was needed. This led to the development of what we now know as the vacuum toilet.

The modern airline toilet was invented by James Kemper in 1975. It went into widespread use in 1982.

The Vacuum Toilet System

The most common type of toilet found on modern aircraft is the vacuum toilet. Unlike regular toilets that use a large amount of water to flush, vacuum toilets use a very small amount of water and a vacuum system to transport waste into a holding tank.

These became more common as aircraft designs advanced, and pressurized cabins became standard.

Stewardess in a pressurized airplane cabin, 1970s. Image courtesy Centers for Disease Control (CDC).

The Flush Mechanism

When you flush the toilet, a valve opens and the vacuum system sucks the waste and a small amount of blue sanitizing liquid (called Skykem) into a holding tank. This is done with great force, which ensures that the bowl is cleared effectively using minimal water.

The force used is about 20 times stronger than the flush of a home toilet. That’s why it’s so loud!

The bowl itself is often made with a nonstick material, almost like a Teflon frying pan. This also helps to ensure that waste can pass easily into the holding tank with minimal water.

Illustration from Kemper’s original patent for airline toilets

The Holding Tank

The waste is transported to a holding tank, which is located in a specific section of the plane. The tank is kept at a low pressure so that the vacuum system can work effectively. The waste remains in the tank for the duration of the flight and is only removed once the plane lands.

No, it doesn’t get jettisoned out the back of the plane! Although some large boats do jettison waste far out at sea, airplanes keep it in their holding tanks until they can land, and the waste can be pumped out and disposed of properly.

Occasionally, the tanks fill up in flight, and planes have to divert to empty the waste!

The Chemical Toilet Option

Some smaller or older aircraft may still use chemical toilets. These do not rely on a vacuum system but instead use chemicals to deodorize and break down waste.

Older passenger aircraft may still use this technique. But it was also common on older military aircraft, too. In this photo from the Imperial War Museum, the canister to the side of the aviator was a chemical toilet.

Chemical toilets today have a reservoir of blue deodorizing liquid under the bowl. When you flush, the bowl’s contents are released into this reservoir where chemicals help to minimize odors.

It’s not as efficient as a vacuum toilet, but on some older aircraft, these systems remain in use and are still serviceable today. A similar system is often used in RVs and some trains.

Environmental and Efficiency Considerations

Airplane toilets need to be both environmentally friendly and efficient. The vacuum toilet system is more water-efficient than regular toilets, which is not only good for the environment but also helps to reduce the weight of the aircraft, saving fuel.

Water is heavy. Every extra pound of weight that an airplane can shave off its takeoff weight results in both fuel savings and environmental impacts.

Thus, vacuum toilets aren’t only about comfort and elimination of smells. They’re also useful because they reduce the amount of water (or chemicals) needed, and thus help to reduce the costs and carbon footprint of flights.

The Cleaning Process

Once the plane has landed, specially trained staff connect the holding tank to a sewage vehicle. The waste is then pumped out and disposed of in accordance with environmental regulations.

Summing it Up

Airplane toilets, especially vacuum toilets, are specially engineered to tackle the unique challenges of high-altitude travel. Through innovative engineering, they manage to effectively deal with human waste in an efficient and environmentally friendly way.

Thomas Smith

Thomas Smith is a food and travel photographer and writer based in the San Francisco Bay Area. His photographic work routinely appears in publications including Food and Wine, Conde Nast Traveler, and the New York Times and his writing appears in IEEE Spectrum, SFGate, the Bold Italic and more. Smith holds a degree in Cognitive Science (Neuroscience) and Anthropology from the Johns Hopkins University.

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