A Catch Basin is a precast concrete box . The catch basin (also referred to as a drop inlet) is an important component in a stormwater drainage system. It is strategically placed underground to prevent flooding of pavement, landscaping, and property. During a rain event, rainwater hits the ground (becoming stormwater) and drains towards the lowest point, the catch basin. As stormwater flows down through the grate, the basin fills. A connected drainage pipe then carries the water downstream. The drainage piping is placed on a progressively downward sloping gradient to encourage stormwater to flow; this is also known as gravity-flow.