March 01, 2019

Airline plumbing systems are kind of a mystery for the casual traveler set. The most obvious questions about them -- especially for those who’ve experienced airborne fecal matter -- goes something like this: What happens after you flush the toilet in an airplane? And why doesn’t the plane keep from leaking those contents across backyard barbecues?

The answers have evolved. And in the case of airline restrooms, they started as systems that now sound downright medieval.

When you fly today, you’re probably sharing a cabin with what’s called a vacuum toilet, a huge improvement over the old blue juice rigs. Inventor James Kemper got the patent on these babies in 1976, and they’ve been on commercial flights since Boeing adopted them in 1982.

There hasn’t been much innovation in the field since then, mainly because the technology works so well. They only use a fraction of the blue sanitation liquid that they used to, and use a vacuum system to siphon waste into a tank rather than leave the work to gravity.

That big, clattery whooshing sound you hear when flushing the toilet is created by the difference in atmospheric pressure outside the aircraft and the cabin pressure within. When you trigger the flush, a valve opens up, and the air pressure sends everything to a tank in the tail of the craft. At low altitude, a blower kicks in, so you can still flush on the tarmac.

The bowl is coated with a Teflon-like material similar to what you’d find on a non-stick frying pan, to aid flushing. From there, it sits in the waste tank until technicians like Miller come and rinse it with ice and vinegar. About once a week, they filter everything into the sewer system.

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