Abstract: Industrial waste water, containing oil, sand and other debris, flows into the separator via a sewer line. In a first phase of operation, solids are separated by mechanical filter means, such as a bar screen, and the water is separated by permitting the oil to rise to the surface of the oil-water mixture in a large settling chamber where turbulence is reduced by various baffles. The water in the settling chamber flows through a passageway formed near the bottom of the tank by a vertical wall extending to the top of the tank. This oil-free water is continuously removed and directed to a settling pool until phase two begins. Phase two begins when the oil floating on top of the water in the settling chamber reaches a predetermined depth. The sewer and water discharge valves are closed. Liquid is then pumped into the bottom of the settling chamber to raise the liquid level in that chamber.