If the toilet is flushed from a tank, a large holding cistern is mounted above the toilet, containing approximately 1.2 to 1.6 U.S. gallons (4.5 to 6.1 L) of water in modern designs. This tank is built with a large drain 2 to 3 inches (5 to 7.5 cm) diameter hole at its bottom covered by a flapper valve that allows the water to rapidly leave the holding tank when the flush is activated. Alternatively, water may be supplied directly via a flush valve or "flushometer".