A sump pump is a pump used to remove water that has accumulated in a sump pit. A sump pit, commonly found in the home basement, is simply a hole to collect water. The water may enter via the perimeter drains of a basement waterproofing system, funneling into the pit, or may arrive because of rain or because of natural ground water, if the basement is below the water table level.
Plumbing drainage and venting systems maintain neutral air pressure in the drains, allowing flow of water and sewage down drains and through waste pipes by gravity. As such, it is critical that a downward slope be maintained throughout. In relatively rare situations, a downward slope out of a building to the sewer cannot be created, and a special collection pit and grinding lift 'sewage ejector' pump are needed.