On a 747 long-haul flight, each passenger uses the toilet an average of 2.4 times, resulting in 870 liters of excrement. This is roughly equivalent to the capacity of a four-person jacuzzi.

There is a huge amount of unwanted material, and processing it all requires miraculous engineering techniques.

This is where the flush function of the airplane toilet comes in handy.

These toilets currently don’t work with traditional siphons and water.

As early as 1982, new toilets began to be installed on airplanes. The toilet featured a non-stick toilet bowl that used a blue substance called SkyChem instead of water, and a powerful vacuum suction device that left almost nothing in the toilet bowl.

Skykem helps to eliminate bad odors and disinfect toilet bowls. What’s more, vacuum toilets use much less water than siphon toilets, are much lighter, and can be installed in a variety of ways, increasing fuel and space efficiency. This is two very important factors on an airplane.

When flushed, the trapdoor at the bottom of the toilet bowl opens, filling it with Skykem liquid. The loud noise you hear when running water is not, as many people think, the sound of a trapdoor opening outside. It’s simply the sound of vacuum suction, like a large vacuum cleaner.

Waste sucked in through holes in the toilet bowl travels through pipes to the rear of the aircraft and ends up in tanks that can only be accessed from outside the aircraft. Even if they wanted to, pilots would not be able to empty this tank in flight.

When the plane lands on the ground, the tank is emptied with a special tanker truck. Tank trucks attach hoses to airplanes and vacuum up waste. When an airplane tank is empty, it is cleaned with disinfectant.

However, in the past there have been a number of accidents in which waste from airplane toilets fell from the sky and into houses.

This was a common problem in the 60s and 70s, when airplane toilet pipes were not sealed properly, causing leaks. Urine and excrement mixed with Skykem and leaked out of the pipes, usually near the rear landing gear and onto the outside of the plane.