Once a flushometer valve has been flushed, and after a preset interval, the flushometer mechanism closes the valve and stops the flow. The flushometer system requires no storage tank, but uses a high rate of water flow for a very short time. Thus a inch (22 mm) pipe at minimum, or preferably a 1-inch (29 mm) pipe, must be used. Water main pressures must be above . The higher water pressure employed by a flushometer valve scours the bowl more efficiently than a gravity-driven system, and fewer blockages typically occur as a result of this higher water pressure. Flushometer systems require approximately the same amount of water as a gravity system to operate (1.6 gpf).