Abstract: A mechanism for releasing a selected volume of water from a tank has a U-shaped bracket which mounts on the interior of the tank via a bushing which passes through a hole in the wall of the tank. A rod is pivotally supported by the bushing and, in turn, supports a valve which mates with the tank drain when the rod is pivoted to raise a valve support arm to which the valve is attached. A key on a latch arm pivotally mounted on the bracket falls into a notch in the periphery of a latch collar on the rod when the rod is pivoted to raise the valve so that water is drained from the tank so long as the key is engaged by the notch. A float collar journally mounted on the rod is positioned by a float as the water level falls to move an electrical contacting member on the float collar along an arcuate path.