Airplane toilets: what really happens when you flush 12km up?

Lulled into sleepy contemplation of clouds while gazing out the window on your holiday flight, you’re pulled out of your reverie by a need to visit the bathroom. That over-priced bottle of plonk from the drinks cart needs to finish its journey from nose to tail. As you finally make your way into the cupboard at the back of the plane, do what you have to, flush and make your way back, perhaps the thought crosses your mind – where does it go to?

Well, the history of the airplane toilet and its contents is filled with a few gross truths and many urban legends. In the very early days of flying, pilots would often relieve themselves in bottles and other receptacles before chucking these out of the window.

During World War 2, many airmen’s accounts include the horrors of the onboard toilet – not much more than a bucket - which would often spill its contents during turbulence. As if the bullets and bangs and veering around in service of the Allies wasn’t enough stress, there was the putrid reek of effluent swashing across the floor to compounded matters.

A similar system remained in place for commercial flights until 1975, when James Kempler invented the no-water, non-stick-coated, Skykem blue liquid system, which first appeared on a Boeing in 1982. Kempler’s system continues to be the standard for most planes today.

When you press the flush button in an airplane toilet, it creates a vacuum - it has been recorded that the speed at which the stuff in the bowl exits is faster than a Formula One racing car. The waste is deposited into a closed system below the bowl.

Contrary to popular belief, there is no way for the pilot to detach the contents of the toilet from the plane during a flight – there’s no button that allows for this and no mechanism that would make it possible. When the poop hits the fan, the waste goes down with the plane.

The bits of waste frozen in blue ice that land on unsuspecting Outback picnickers are not the result of sewage that has been flushed straight out of the toilet into the sky but rather of leaks that result in seepage from the closed waste system, which freeze at altitude, attach themselves to the fuselage and then kind of melt off as temperatures reduce.

On average, long-haul flight passengers visit the toilet 2.4 times and produce around 833 litres of waste per flight, according to The Points Guy. That’s a lot of poop and it’s only once the plane lands that it is disposed of.

The “toilet acquisitions”, are vacuumed into another tank on the back of a truck. When that tank is full of waste from various flights, it’s emptied out. The only mystery is where, exactly? On this point, no one is quite sure.