Just started working in facilities maintenance, I deal with toilets a lot but don’t understand the magic completely.
In: Engineering
Behind the bowl is a pipe shaped like an “S”. As the flushing action starts and water fills up the bowl, the pipe starts to fill up as well. When it gets to a certain point, the pipe pulls on the water and waste in the bowl and into the drain it goes. The rest of the flushing action then refills the bowl.
The magic is in the water pressure. Once a certain water weight is achieved, it gravity takes over and provides suction to the bowl, letting it pull whatever is in the water with it
Older style toilets – water fills the bowl until the level is higher than that of the drain. Once that happens, the water sucks all your “stuff” down the pipe just like siphoning works. (Put a pot of water up high and stick a tube in it with the other end lower than the pot, suck on the tube until water flows and watch the pot drain completely.)
Newer toilets – there’s a “jet” that kickstarts the above process by forcing water directly into the drain rather than waiting for the bowl to fill.
A toilet is fundamentally a bowl with a hole in the bottom, and a pipe coming from the hole which first curves upward a bit before going down to the sewer.
As long as the water level in the bowl is lower than the height of the upward-curving drain pipe, the water just sits in the bowl.
If you add a small amount of water or other stuff to the bowl after it reaches the height of the pipe, the extra water spills over the edge of the drain pipe into the sewer and the water level in the bowl remains constant.
However, if you add a large amount of water to the bowl at once, this completely fills up the drain pipe. This means that water falling into the sewer will leave behind vacuum rather than air, creating a siphon effect; all of the water in the bowl (and everything in the water) is sucked down into the sewer. This is called a “flush”.
You can flush a toilet bowl manually by pouring a bucket of water into the bowl, and then refill it manually by pouring some more water into the bowl.
However, the toilet tank is designed to automate both the flushing and refilling processes. When you pull the lever, the water in the tank is dumped into the bowl, causing a flush. Inside the tank is a float that detects water level in the tank; when it detects that the water level is low (i.e. that the toilet has just been flushed), the float activates a faucet that adds water to both the tank and the bowl, refilling them.
The diagrams on [this site](https://www.1tomplumber.com/toilet-flush-is-slow/) are fairly clear if you’d like to see a visual.
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