Siphonic Action
From Toiletpedia
Siphonic action is the "pull" created when the toilet is flushed, and water rushes into the S-shaped trapway or colon behind the toilet. When water reaches the top of the trapway—called the “weir”—gravity pulls it into the downward leg of the S. 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 siphon action to cleanse the bowl.
Also See:
Images:
Toilet Diagram- from renovation-headquarters.com
