How Do Sewage Pumps Work?

Paul Favors

In a sewage system, gravity allows liquids and solids to move down a line, transporting waste matter between locations. In cases where gravity power is not possible, such as when a plumbing line goes uphill or horizontally, a sewage pump is needed to effectively move the sewage matter from one place to another.


Typically, the sewage pump is placed at the bottom or near the bottom of the sewage basin, which is subsequently found on the lowest part of the area that needs to be drained. Most of the time the sewage pump is submerged in the basin. As such, it is referred to as a submersible sewage pump. A submersible sewage pump is placed at the bottom of the receptacle, such as in the case of a septic tank. The pump’s intake is located as close to the bottom of the receptacle so that the liquid and solid contents of the basin can be emptied once the pump is switched on and powered. Total draining of contents, however, is unlikely to happen because there has to be some room between the floor and the sewage pump in order to effectively release air pressure. Thus, manual intervention is still needed to completely empty the contents of the basin.


Whether residential or commercial, most kinds of sewage pumps work on the same principle. Like a sump pump, a sewage pump has a bulb attached to it, similar in mechanism to a toilet reservoir. When the bulb reaches a certain point or height, the switch is triggered and the pumping action starts. Once the liquids are drained and the basin emptied, the bulb lowers to a certain point, which then automatically switches off the pump.

Power and Size

The power of a sewage pump is usually rated in horsepower with a range between half a horsepower and one horsepower. The size of the pump is determined based on the amount of sewage that needs to be transported, which is expressed in gallons per hour.


A sewage pump usually handles mostly liquid or mashed waste, but there are times when solid wastes have to be disposed off through the system, such as when a bottle cap or plastic tube is flushed down the toilet. Most residential pumps can handle up to 2 inches in diameter of solid waste while commercial pumps can handle even larger solids. When a relatively larger solid object (larger than the capacity of the tubes and pump) is flushed down the toilet, it could get stuck and obstruct the flow of the waste even with the help of a sewage pump, causing the pipes to clog. In this case, one would have to call a plumber to fix the pipes.