At first sight, the modern toilet seems quite simple: you have a waste pipe going through the floor and a tank of water up above (a cistern) waiting to flush into it when someone pushes a button. Most flush toilets are purely mechanical: push the button and the cistern empties through the force of gravity, washing the bowl clean for use again. They are mechanical as they flush and refill using levers inside. Here is what happens on the inside when you press the button:
1. Push the button to flush the toilet and you move a lever inside the cistern.
2. The lever opens a valve called the flapper that allows the cistern to empty into the bowl beneath through a mechanism called a siphon.
3. Water flows from the cistern through holes in the rim of the toilet bowl so it washed the bowl as well as flushing the contents away properly.
4. There is enough water flowing down from the cistern to flush the contents around the S-bend, producing a siphon effect that sucks the bowl clean. It also ensures some water remains at the bottom of the toilet, improving hygiene.
5. The contents of the toilet then continue to be flushed to the main drain.
6. As the cistern empties, a plastic float falls downward, tilting the lever.
7. The tilting lever opens the ball valve at the base of the cistern, water flows in refilling the cistern, and pushing the float back up again. When the float reaches the correct level, the ball valve switches off the water supply and the toilet is ready to flush again.
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