Inlet Check Valve for TSL fluid bottles. Arrows on the side of the valves indicate the flow direction. An end is cut off one check to make it more difficult to hook them up backwards. Putting them in backwards causes the checks to break.
Flush your current TSL fluid lines and the pump with WD40.
DO NOT USE Carb cleaner, Acetone or other solvents. They damage the hose and pump seals.