Welcome to Brainstuff from how stuff works dot com where smart Happens. Hi'm Marshall Brain with today's question, how does the toilet and a commercial airliner work? If you've read the house stuff Works article entitled how toilets Work, then you know my philosophy on this kind of stuff. Toilets have a very bad image because of what we put into them, but if you can get past that and focus on the technology behind them, toilets can be pretty
amazing devices. The typical home toilet uses a bowl filled with water. When you flush the toilet, it starts a siphon that drains the bowl. Gravity then carries the water into the septic tank or the sewer system. The problem with this approach on an airplane or a train, or a bus or a boat or whatever is that the motion of the vehicle means you can't use a bowl of water. It would splash out every time there was
a little turbulence. Since there is no bowl of water, you can't use a siphon or gravity to empty the bowl. So airplane toilets use an active vacuum instead of a passive siphon. They're actually called vacuum toilets. When you flush, it opens a valve in the sewer line, and the vacuum in the line sucks the contents out of the bowl and into a tank. Because the vacuum does all the work, it takes very little water or that blue sanitizing fluid used in airplanes to clean the bowl for
the next person. Most vacuum systems flush with just half a gallon or two liters of fluid or less, compared to the one point six gallons or six liters of water for water saving toilets and up to five gallons for an older toilet. It turns out that vacuum toilets have lots of other advantages even in normal installations. They do use very little water, They can use much smaller diameter sewer pipes. They can flush in any direct action,
including upward. Sense a vacuum system doesn't use gravity to move the water, there's nothing to stop the sewer pipe from going straight up, and they can be put anywhere in the building. For more on this and thousands of other topics, because it how stuff works, dot com