How do toilets work? Quite well! Okay, now my obligatory “dad joke” is out of the way, let’s figuratively dive in to your basic home toilet, water closet, or loo.

There are two major sections of a toilet: the tank which holds water for flushing to handle active work, and the bowl, which is passive. The toilet bowl is simply a porcelain bowl that attaches to a 3” or 4” drain pipe in the floor. Between the bowl and the floor is an S-trap, which holds water in the bowl between uses. Just like your sink’s P-trap, the S-trap is a physical barrier to keep sewer gasses from escaping into your bathroom. It also serves the purpose of emptying the toilet when you flush.

When sufficient water is added to the toilet bowl, water rushing down the drain pipe creates a pressure differential similar to a vacuum. The water exits the drain pipe fast enough that it pulls more water from the toilet bowl, and completes the cycle until water is emptied from the bowl. After the bowl is empty, air can flow through the pipes and equalizes pressure, so there is no more pressure vacuum acting on the bowl. Picture a clean, fresh, new toilet with no tank attached that contains water in the bowl. You could “flush” the contents of the bowl by quickly emptying a two gallon bucket into the bowl, and most of the water would drain away quickly. But if you slowly add two gallons of water, it will simply flow past the S-trap, not create a pressure differential, and you would neither fill nor empty the water in the toilet bowl. That is basically all there is to a toilet bowl – a container and an engineered S-trap that works around natural forces.

The toilet tank handles all the active parts. Looking at the simplest of toilets (and there are some advanced ones on the market), it is a tank of water with controls to empty and refill that water. It includes a fill valve which connects to a supply pipe and controls how much water is filled for flushing. Some kind of floating bobber connects to the fill valve and will turn off water once your desired water level is reached. Then we have a flush valve – essentially this is a plug to keep the water in your tank. Push the flush handle and it lifts the plug, so water rushes into the tank to empty the toilet bowl. When most of the water has left the tank, the flush valve plug will re-seat itself with gravity, water will fill the tank and the pressure from water will keep the plug in place until the cycle repeats at the next flush.

Newer toilets use more mechanisms to allow flushing with less water, smarter designs flush better with less water, and there are many varieties on the market – but essentially, those are all the components of your toilet. It’s an essential fixture in homes, but one that has changed very little since its invention.

Too Long, Didn't Read Version: Toilets are so vital to modern, hygienic living that we often assume they are complicated. Instead, they use simple physics to serve their purpose with very little appreciation. You may not be comfortable adjusting a toilet that constantly fills, but the simple nature means it won’t take a plumber long to correct issues for you.

-Marshall Tramp, CPI, RMP

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Marshall Tramp, CPI, RMP
Author: Marshall Tramp, CPI, RMP
Top Notch Inspection Services llc
Serving Eastern Washington & Northern Idaho