Abstract: A mobile separator system for receiving and separating a mixed composition of oil, water, and sludge. The mobile separator system including a tank for holding the mixed composition, and a drain manifold that includes a plurality of drain pipes extending into the tank at varying elevations for allowing the drainage of water from the tank system. A vacuum source is attached to the top of the tank for carrying a vacuum within the tank to draw the mixed composition into the tank. The drain manifold is surrounded by a screen that allows the passage of water and oil, while preventing the passage of sludge through the screen into the drain pipes. A floating check valve is connected to each of the drain pipes to regulate the flow of water through the drain pipe. The floating check valve includes a valve element that has a density which causes the valve element to float in water and sink in oil.