How Does an Airplane Toilet Work?


I’ve been writing on some weighty topics lately — multi-billion-dollar deals, air traffic control, Grand Teton National Park. It’s time, I decided, to move on to a question that haunts me almost every day. How does an airliner toilet work?

In North America, the standard is one lavatory for every 50 passengers. It’s a much better ratio in business class, but strangely no airline uses that as a selling point. Nor do they serve blue-colored Gatorade onboard.

But that Gatorade-blue liquid is mostly history. Manufacturers have moved to vacuum flush technology patented in 1975 (less weight, less odor) and first installed by Boeing in 1982.

The old siphon toilets rely on a liquid-filled bowl that push waste (with the aid of electric pumps) into onboard storage tanks. But planes had to haul hundreds of gallons of irritant liquid (formaldehyde and bleach-based).

And that old system with its corrosive chemicals was prone to leaking. Gobs of blue-icy “stuff” could work its way to the exterior of the plane. On approach, as altitude dropped and outside temperature rose, the frozen blue “stuff” could break away and skydive to Earth.

Between 1979 and 2003, at least 27 wads of “blue ice” fell from the sky in the U.S., often landing with enough force to cause damage. Here’s a report of it ripping through a roof.

The airlines wanted a fluid-free alternative. Inventor James Kemper solved the problem while establishing more than 50 U.S. patents en route to awfully loud vacuum toilets with strong suction and non-stick bowls.

Pressing the flush button opens a valve in the bottom of the bowl and a pneumatic vacuum sucks the load down the plane’s sewer line into a holding tank. Waste remains in the tank and gets vacuumed out by crews on the ground.

(At this point, my source for this information said “an exterior latch on the holding tank ensures that pilots don’t accidentally drop a load in mid-air.” I just kept on writing and only now get his point.)

Variations of the Kemper system remain the industry standard.

Airbus has an entire research lab built to fine tune A380 toilets. It’s “Formula One technology” where waste can reach speeds of 130 miles per hour. As they say, it’s a feat of engineering not to be sniffed at.

Mythbusters on Discovery tested the myth about a toilet sucking a person into the bowels of the plane. It’s myth.

The Tarmac’s View:  Trivia question – Why do your ears sometimes feel pressure changes when you flush an airline toilet? Because the vacuum flushing may cause the pressure altitude within the tiny lavatory to quickly jump 5 to 20 meters.


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Comments (Showing 2 of 2)

  • laggers at 11:13pm August 02, 2013

    We don’t care HOW it works, ONLY that it does work.

  • Asiaflyguy at 11:40pm August 03, 2013

    i would rether read this than about why it take so long to board an airplane, for the 100th time in the past month… that dog just wont hunt anymore…

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