A sump pit is the below-grade enclosure that houses the sump pump. As water accumulates in the sump pit, the float-activated switch of the pump engages and pumps the water out of the pit and away from the pit site. Water enters the sump pit through a number of controlled systems, depending on the water situation at the site.
Perforated tiles placed horizontally below the ground are sometimes referred to as drain tile. The low end of the tile system leads to the sump pit. The system collects water from the entire area of the drain tile system so it can be pumped away from the site where it will do no damage. The most common drain tile scenario is around the foundation of a house, although it can be used in other situations where subsurface moisture needs to be removed.
The sump pit is commonly made of 16- or 18-inch PVC pipe placed vertically with a cement bottom. If the PVC pipe is perforated, water from the immediate area flows into the sump pit. Fill the area around the PVC pipe with crushed rock or gravel to prevent soil from washing through the perforations into the sump pit. Soil-laden water can damage the sump pump. This configuration extracts water from a limited area compared to the drain tile system.
In some situations, ground water runs over the edge of the sump pit. This configuration works with surface water rather than the subsurface ground water of the drain tile or perforated pit systems. Think of this as a sump pit placed in a basement floor. Water in the basement drains into the sump pit and is pumped out. This system limits damage but doesn't prevent flooding.
It’s All About Gravity
Any system of drains and sump pits works by gravity. The pumps do not draw water up from lower levels of the soil but rather remove the water above the drain tile and the sump pit. For this reason, the sump pit must be located below the subsurface level of any materials or structure you need to keep dry.