Travel & Day Trips

What Happens When You Flush an Airplane Toilet?

Airplane toilets have been a marvel and a source of curiosity for many. Their loud flushes often leave passengers wondering where everything goes. In this post, we will uncover the mystery behind what happens when you flush an airplane toilet.

The Flush

Airplane toilets are different from the ones we have at home. Instead of using a large volume of water to flush, they use a vacuum system. When you flush, a valve opens, and the vacuum sucks the waste into a holding tank. The strong sucking sound that you hear is because of the rapid air movement due to the vacuum.

Holding Tanks

The waste doesn’t just disappear into thin air; it goes into a holding tank. Airplanes have designated holding tanks for waste, which are situated at the bottom of the aircraft. These tanks are built to be leak-proof and are equipped with sensors to indicate when they are nearing capacity.

Blue Deodorizing Liquid

You might have noticed that the toilet water in airplanes has a blue color. This is due to a special deodorizing liquid that is added to the holding tanks. This liquid helps in breaking down the waste and controlling odors.

It’s called Skykem.

Disposal on the Ground

When the plane lands, one of the tasks of the ground crew is to empty the waste from the holding tanks. Specialized vehicles with hoses connect to the sewage system of the aircraft to pump out the waste. The waste is then transported to a treatment facility.

Environmental Considerations

Modern aircraft toilets are designed with environmental sustainability in mind. Earlier models of airplane toilets used more chemicals, but with advancements in technology, the newer vacuum systems are more efficient and environmentally friendly. Additionally, measures are taken to ensure that the waste is disposed of according to environmental regulations.

Myth Busting: The Blue Ice Incident

There’s a common myth that waste is jettisoned out of the aircraft during flight. This is untrue. However, in the past, there have been rare instances where leakage from the holding tanks formed frozen masses called “blue ice.” These would sometimes detach from the aircraft. Modern airplanes have much more secure and advanced waste systems to prevent such occurrences.


The next time you use an airplane toilet, you can do so with the knowledge of what actually happens after you flush. With technological advancements, these systems continue to evolve to be more efficient and environmentally friendly. The entire process from flush to ground disposal is a testament to human ingenuity and consideration for environmental sustainability.

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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