Eli5 what happens to our waste when we use the bathroom on a plane and why is it so loud?
In: Engineering
It gets sucked into a septic tank. The tank is then emptied by a ground service vehicle once the plane lands.
The interesting part is that on the ground and below an altitude of about 14000ft (varies by plane type), the noise comes from a vacuum generator that sucks the waste into the tank. The vacuum generator is like a very powerful vacuum cleaner engine, so it makes a lot of noise.
Above that altitude, the differential pressure between the cabin (where you can breathe) and the unpressurized tank (outside pressure) is so large that the waste is sucked down by just opening the seal at the bottom of the toilet. The noise here comes from the air moving rapidly through a tube that gets tighter and tighter.
An unrelated fun fact is that the oxygen percentage is the same at high altitudes as on the ground. It’s the lack of pressure at high altitudes that make our lungs unable to use that oxygen. That’s why the cabin on an aircraft is pressurized with air rather than pure oxygen. When people say there’s less oxygen at higher altitudes, they’re actually wrong.
Source: I work as an airline pilot.
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