The mechanisms within conventional toilets have not changed much since they were invented, but recently, a new generation of toilets has become available. Pressure-assisted toilets use compressed air to move waste products, rather than relying on gravity to do the work. This means that the bowl is typically cleaned more quickly and thoroughly, using less water.
Traditional, or gravity, toilets work in a very straightforward manner. Water is stored in a tank above the bowl and when the flush lever is pressed, the water is released under the force of gravity into the bowl and the waste is removed. From the outside, pressure-assisted toilets look identical to gravity toilets, but when someone lifts the lid, however, instead of seeing water, he will notice an inner tank.
The tank is completely sealed; when water is fed from the water line, the air inside the tank gets compressed. When the toilet is flushed, instead of just falling by the force of gravity, the water is forced out with the pressure of the compressed air. This pressurized stream of water cleans all the waste from the bowl much more efficiently than the water from gravity toilets. The pressure in the toilet is created by using the water pressure provided by the water company — no pumps or other devices are used.
Pressure-assisted toilets are more expensive than gravity toilets, but they do a better job of removing waste from the bowl with less water. The first generation were very noisy and some were not very reliable, but most of these hurdles have been overcome.