The typical home toilet is a bowl filled with water… as I imagine you know. When you flush that toilet, gravity pulls pulls the water down the pipes and into the the sewer system. Because gravity is a major player, your home toilet is called a gravity toilet.
However, an airplane can’t use a bowl filled with water — or, at least it can’t do it very conveniently. Every time the pilot hit turbulence, the lavatory would be covered in water.
Instead, modern airplane toilets are vacuum toilets. The flush works in two stages. First, a small quantity of water is is released. Second, a powerful — and often frightening-sounding — vacuum is activated for a few seconds. During that unsettling sucking sound, a valve in the sewer line opens, and the vacuum in the line sucks the contents out of the bowl and into a tank, which is later cleared out by a lavatory service cart.
[Photo: TheMachineStops]