Abstract: An emergency shut-off for a flush tank having a liquid replenishment valve is connected to the liquid replenishment valve for moving the valve to a closed position if liquid level in the tank has not reached a predetermined height within a predetermined time after the tank has been flushed. Broadly speaking, the emergency shut-off comprises a container, a buoy, and a valve connection mechanism. The container extends downward in the tank from at least the predetermined height and includes a valve for allowing liquid in the tank to enter the container and for allowing liquid within the container to egress into the tank at a predetermined rate. The buoy in the container raises and lowers with the liquid level in the container and contacts the valve connection mechanism when the liquid in the container is at a predetermined shut-off height. The valve connection mechanism is connected to the valve for closing the valve in response to contact by the buoy.