Flushology 101 How Toilets FlushBy
It may not be rocket science, but a good toilet flush is a lesson in physics.
When the toilet is flushed, water fills the toilet bowl and the upward leg of the trapway, the S-shape visibly snaking out the back of most toilets. When water reaches the top of the trapway, called the weir gravity pulls it into the downward leg of the S. Hence the name, gravity fed or simply gravity toilet.
The rush of water running downhill pulls waste and water out of the bowl. The stronger the push of the water, the stronger the pull of siphonic action to cleanse the bowl.