A circular disk covered in rubber or plastic with a hole in the center where the edge is sometimes tensioned by a spring that prevents fluid from leaking at the Windshield Washer Fluid Pump. Washer Fluid Reservoir Cap Seal. Windshield Washer Pump Grommet. Fluid Reservoir Cap. Windshield. Included with: Battery tray, Reservoir assembly, Washer Reservoir, Washer Reservoir assembly.