Submersible pumps have numerous uses, due to their ability to operate underwater.
They work by protecting their motors from whatever liquid is pumped, be it water, sewage or otherwise. Usually, motors are housed in an oil-filled water-tight compartment.
The pumps don't rely on external pressure to operate, and instead rely on a system of mechanical seals to prevent the pumped fluid from entering the motor.
Submersible pumps have a wide variety of functions. They are often used for drainage, industrial pumping, sewage pumping and slurry pumping. Multiple stage submersible pumps can be used for water abstraction and in oil wells.
The pumps come in various strengths and are usually effective in pumping all sorts of liquids, however viscous levels at great depths can cause pressure problems. In this instance, it's best to hire the strongest pump you can.
Occasionally, pumping will bring up debris with the liquid, so make sure your pump hire is one that can handle solids. Usually these types of pumps will have an agitator or spray hole in order to mix firm particles in with the liquid, enabling the machine to pump them out of the ground more easily.