Cummings' innovation was an S-shaped double bend in the waste pipe. Water would remain in this bend, called a "trap", forming an air lock that isolated the air near the toilet from the sewer gases down in the main sewer pipe. Most all plumbing fixtures today have a similar drain line...
Most toilets rely on gravity to clear the bowl when the toilet is flushed. As water rushes into the bowl from the storage tank, the force of the water pushes the standing water over the horizontal bend of the trap. This creates a siphon or sucking action that pulls the contents of the ...