The Mainstream Pumping Station, located in Hodgkins, Illinois, is one of three stations in the Tunnel and Reservoir Project designed to capture combined sewer overflows from an area of 375 square miles.

The Station serves as part of the Tunnel and Reservoir System which is designed to prevent backflows into Lake Michigan, eliminate waterway pollution caused by combined sewer overflows and provide an outlet for flood waters.

The Mainstream Tunnel System consists of 31 miles of tunnels, 13 to 33 feet in diameter and 240 to 300 feet below ground. It extends from Wilmette, Illinois, in the north to McCook, Illinois, at its southern end. Sewage and stormwater entering the tunnels through drop shafts are carried to the Mainstream Pumping Station, where the flow is pumped to the District's Stickney Water Reclamation Plant, Stickney, Illinois.