All surge tanks, receiving reservoirs, gravity storage tanks, house storage tanks, or tanks of any description used for receiving or storing city water at atmospheric pressure, shall be supplied an approved slow-acting automatic control valve. The discharge outlet of the control valve shall be directly connected to the receiving unit at a distance of 6 inches (150 mm) above the top of a horizontal overflow pipe. For a vertical overflow pipe, the distance shall be 6 inches (150 mm) plus the diameter of the overflow pipe. The overflow pipe connection shall have an area of not less than twice that of the supply opening.