Why Aircraft Toilets Are So Loud When Flushed

It should go without saying that the sound of a toilet flushing on an airplane is deafening. Considering the aircraft’s ventilation system and engines combined are already providing enough ambient noise to drown out a normal speaking-level-conversation, the fact that a toilet’s flush pierces through these sounds and can be heard halfway through the cabin, it’s an understatement to call this noise ‘loud.’ But why is an airplane’s toilet flush so much louder than the average household toilet?

Why Aircraft Toilets Are So Loud When Flushed
The loudness of an aircraft’s toilet flush is roughly equivalent to being one or two meters away from a chainsaw or standing on a platform and being passed by a moving train. Photo: Getty Images

According to the Wall Street Journal, the toilet is essentially the loudest part of the flying experience, reporting that crew announcements typically come in between 92 and 95 decibels. In comparison, toilet flushes hit 100 decibels – along with forceful overhead bin door slams. Surely there is a good explanation for this.

So why are aircraft toilet flushes so loud?

Simply put, the flush’s loudness is due to a partial vacuum that sucks the contents of the toilet bowl down into the aircraft’s waste tank. Whereas your standard ‘ground toilet’ is drained with the release of five to ten liters of water, it’s not so feasible to dedicate so much space and fuel to carry this much water for toilets in the sky. And then, of course, there would be the messy issue of spillage during take-off, landing, and turbulence!

It’s probably unnecessary to include an example. Still, just in case you didn’t know the sound of an aircraft’s toilet flush (or, more likely, forgot after having spent so much time on the ground), here’s a video clip for your convenience:

According to The Points Guy, the modern aircraft toilet was invented by James Kemper, who patented the vacuum toilet in 1975. This invention was then installed on Boeing planes by 1982. Instead of using the conventional combination of water and gravity, a vacuum is used to move water and waste at high speeds down to the waste tank. According to the CBC, flushed contents can move at high speeds of up to 150 meters per second — or 300 miles per hour!

Aircraft lavatory toilet
Aircraft toilets are also covered with a non-stick coating to ensure the bowl is emptied completely. Photo: Tiowiafuk via Wikimedia Commons 

Down to the waste tanks

As you may know, the passenger cabin of an aircraft is pressurized to a lower altitude. The aircraft’s toilet system includes a valve that maintains that pressure difference. Upon flushing, the valve opens, and then this waste is sucked down tubes that fill up the tank.

Depending on the size of the aircraft, there are one or more tanks located at the rear of the plane, underneath the floor. The toilets connect to these tanks via piping that is installed all the way down to the end of the aircraft. Therefore, whenever someone upfront in first or business class flushes, those contents are being moved at high speed to the back of the aircraft.

Aircraft lavatory waste removal
Part of the time an aircraft spends at the airport gate usually includes emptying of its waste tanks. Photo: mnts via Wikimedia Commons 

It probably also doesn’t help that you usually have the lavatory door closed when you hit the button to flush the bowl. As the soundwaves have few places to go, this would inevitably intensify the flush as they bounce around the confined space.

Are you good at coping with the intense sound of an aircraft toilet flushing? Do you ever cover your ears? Let us know in the comments.