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What Happens When You Flush a Toilet?

It’s a wonder of modern technology with many names: the throne, the john, the loo, the porcelain princess. Chances are, you have flushed a toilet today. Maybe more than once. Flushing is one of those everyday conveniences that we can’t live without. But how does it work? Let’s take a moment to look out how this expeller of excrement does its thing.

Pulling the Handle

If you have ever looked ‘under the hood’ of your toilet, you have seen the simple machines that make flushing possible. The process starts before you lift the lid. The first part of the flushing mechanism is the handle. This familiar apparatus acts as a lever that pulls up as you push down. The handle is normally connected to a tank lever that yanks on a chain connected to the flapper. It is kind of like a wet game of Mouse Trap, if you think about it. The flapper is a plunger-like stopper that keeps the water from leaking down the flush valve into the bowl. Once the flapper is lifted, water is free to flow down. This causes the rush of water that results in the flush (we’ll talk about the mechanics of the flush later).

When the water leaves the tank, a device tells the toilet’s internals to start filling up again. This can be either a large rubber float (that looks kind of like a balloon) or a float cup. Both devices are attached to the toilet’s fill mechanism and tells the fill valve when to open and when to close. Once the float device reaches a certain height, the valve closes. If the toilet is not set up correctly, and more water enters the tank than it can hold, water goes into the overflow tube. It is important to make sure that the water reaches the correct level and is not too far above or below the indicated fill line.

Facts About Flushing

Toilets are powered by the wonder of fluid mechanics. Flushing is caused by water flowing into an S or U-shaped pipe connected to the bowl called a siphon pipe. When the water volume reaches the point when it flows into the siphon pipe, fluid mechanics causes the water to be sucked down into the sewer system.

But why does the water spin as it drains? Isn’t this somehow related to the rotation of the Earth? Despite being an idea spread through popular culture, the rotation of water in a toilet is governed by the way the toilet was designed, not because of Coriolis forces. An article from The Atlantic debunks the popular myth. Coriolis forces are better observed on a large scale with phenomenon like hurricanes, not something as small as a toilet.

How Much Water Does It Use?

The amount of water used in every flush varies from toilet to toilet. Older toilets may use up to a whopping 7 gallons per flush. Efforts to conserve water have led to the creation of low flow toilets. lists the best in High Efficiency Toilets (HET) at being able to handle carrying away waste with as little as 1.28 Gallons. Some toilets even come equipped with two flush volumes. A small amount of water is used to flush fluid waste while a larger amount is used for anything solid.

What Not to Flush

Toilets are designed to carry away human waste and the toilet paper we use to clean ourselves. Yet somehow other objects end up going down the tubes. While it may be tempting to toss things that look the same as toilet paper into the bowl, it is best not to. Products designed for use in a toilet are always clearly marked as safe to flush. Putting anything down the drain that is not meant to be flushed risks clogging the intricate system that makes flushing possible. Even if an object makes it passed the siphon pipe, it may combine with other matter to form a clog somewhere down the line.

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