What happens when you flush a toilet on an airplane? –Lily, age 6, Harcourt
Lily, this is a great question! It doesn’t work like your toilet at home, that uses gravity to take waste from our toilets to the sewer system. An airplane toilet uses a vacuum system along with a blue chemical that cleans and removes odors every time you flush.
A smelly tank
The waste and the blue cleaning fluid end up in a storage tank under the floor, at the very back of the aircraft’s cargo hold. With so many people on the plane using the toilets, you can imagine how big the storage tank is!
The system is much like the vacuum cleaners we use around the house to remove dirt and dust from our floors. This dirt and dust ends up in a container that we empty into a garbage can. Similarly, the aircraft’s toilets require the vacuum pressure system to move all waste from the toilet to the drain line that connects the toilet to the holding tank, and finally into the tank.
There is a valve on the storage tank that opens when a toilet is flushed and closes when the toilet is not in use – to prevent odors from leaving the tank. This helps to limit the stench of so many people going to the toilet during a flight. The blue chemical also helps keep the odor down.
Where does it go when the plane lands?
a special truck comes to the plane after it lands and connects a hose to remove the waste and blue cleaning chemicals in a storage tank on the truck. The truck connects a hose to the valve of the aircraft waste tank and removes all waste in the tank at the back of the truck.
The truck then takes the waste to a special area at the airport reserved for all aircraft waste and the toilet waste is emptied into that airport’s sewer system. The training to operate the truck takes three days.
Different trucks and vehicles will maintain the aircraft, load fuel, load cargo and collect garbage at the airport.
aapp/Shutterstock
Watch out for blue ice
It has also been reported that sometimes, especially on older aircraft, the flap where the garbage truck connects to the aircraft may leak a small amount of the waste and the blue chemical. This turns into ice because the temperature at normal cruising altitude of 30,000 feet is normally around -56℃ and the chemical changes to “blue ice”. This blue ice remains attached to the aircraft as long as the temperature remains below freezing.
Once the plane begins to descend to land at the destination airport, the blue ice begins to thaw and may even fall off. There have been several occasions reported in the news where people have seen this flying poo!
In case you’re wondering, the plane’s captain doesn’t have a button to release the waste from the holding tank while the plane is flying. Any debris that could leak from the plane would be completely accidental.
Some people think so airplane contrails (the white lines that planes sometimes leave in the sky) are either a special mind-control chemical or toilet waste. This is not true! What you actually see are water vapors coming out of the engine ice crystals – like a thin cloud in the sky.
Read more: Curious Kids: where do clouds come from and why do they have different shapes?