Pump toilets and flush valve toilets do not work in the same way. The flush valve toilet is a relatively simple device that works because of gravity, and it generally works extremely well. The pump toilet does not rely on gravity, but uses mechanical means to move waste. Certain situations may require the pump toilet's unique ability to move waste in a direction other than down.
When it is Necessary
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A pump toilet is often called an up-flush toilet. This is due to its ability to move waste sideways or even upwards. A gravity toilet must always be above the sewer pipes it is draining into, but that is not the case with an up-flush toilet. Situations where a toilet pump is called for include basements where the floor is lower than the existing sewer line and rooms where it would be difficult to run sewer lines under the existing floor.
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The Flush
A toilet pump commode appears to flush in the same way as a standard toilet. The water from the water tank pushes the waste from the bowl into the pump tank located behind or off to the side of the commode. The waste water flowing into the pump tank also starts a grinder motor.
The Grinder
An up-flush toilet cuts the waste into smaller pieces with a grinder blade, called a macerator. It is necessary because up-flush toilets use a much smaller discharge line than a regular toilet -- usually 1 inch compared to 4 inches. The macerator is able to handle most waste and paper, although things such as diapers or condoms should not be flushed. The macerator is sealed and should not need servicing. It accomplishes its task in 4 or 5 seconds.
The Pump
As the name suggests, there is also a pump in the pump tank. After the macerator finishes its task, the pump kicks in to move the waste water out of the system. The pump is electric and therefore fairly quiet. The pressure generated by the pump allows the toilet to push the waste water horizontally or vertically. After the pump has moved the waste out, the pump turns off and the toilet is ready for use again. The whole process takes less than 20 seconds.