Abstract: An apparatus for maintaining a predetermined liquid level within a tank while effecting the continuous addition and removal of liquid within the tank. The apparatus is provided with a housing that mounts directly on a side wall of the tank with the housing extending on both sides of the wall, so that it is partially inside and partially outside the tank. The housing has a first passageway which receives fresh liquid from a pressurized supply and introduces a portion of the fresh liquid into the tank. The remainder of the fresh liquid is provided to a second passageway which is connected between the first passageway and a drain. The second passageway has a constriction near its inlet, which accelerates liquid flowing through it and injects the liquid into the second passageway at a high speed. This produces a region of low pressure in the second passageway. A third passageway is connected to the region of low pressure and it is coupled to the water in the tank.