Aircraft toilets don’t work the same as those on the ground. Storing so much water would need extensive and heavy water tanks, and imagine the problems with water-filled toilets and turbulence! Instead, they use a vacuum system, as this article explores.
Early aircraft toilets
In the early days of aviation, toilets (if there were any) were quite different. Some of the luxurious flying boats had a full size, water-based flushing toilets. Chemical toilets soon appeared, though. There date back to the 1920s, with British company Elsan developing some of the earliest ones.
Chemical toilets flush using a disinfecting chemical mixed with a minimal supply of water. This requires large tanks, usually located near the bathroom.
Remains the standard used on modern commercial aircraft.
Toilets have a nonstick coating, which is emptied by suction. There is no water flush, just this suction. There is some liquid flushed through, usually blue disinfectant liquid (known as Skychem), but no continuous water passed through. This means only relatively small tanks are needed to store the disinfectant and the waste. And there is no water-filled system to slosh around.
How does the flush work?
The toilet suction works by pressure difference. The toilet bowl is connected to the waste tank, which is kept at a lower pressure. In the air, the pressure difference is created using the more downward external force than the pressurized cabin. When on the ground, there is a pump used to create a vacuum.
When the toilet flush button is pressed, the Skychem solution is first passed into the bowl. A valve then opens at the toilet base, and the contents are sucked out to the storage tank by the vacuum created. This is a rapid and robust suction. And it is what causes the loud noise whenever the toilet is flushed.
What can go wrong?
The toilet system may seem like a simple design, but it works well. There have been few changes made over the years since the 1970s. Toilets have changed, either more significant and more luxurious in first-class or evermore minor. More passengers are packed on narrowbody aircraft Toilets, and bathrooms may have improved on many aircraft.
Contrary to some scare stories, it is impossible to be sucked into the toilet by the suction created. Nor do frozen pieces of toilet waste end up falling to the ground. There have been some cases of liquids leaking from the system and either falling to the ground as ice or damaging parts of the aircraft, but this is rare.
And as a final thought, the aircraft toilet may not be a dirty as you would think. Some exciting research during the coronavirus pandemic highlighted the most contaminated parts of the aircraft that passengers come into contact with. Topping the list is the seatback table, up to ten times worse than the toilet areas.