Niagara Conservation Water Saving Toilet Tank Bank he Tank Bank is the easiest device to use to save water - fill to top, snap to close and hang in toilet tank. Every flush saves water with maintenance-free toilet tank displacement bag; up to 0.8 gallons per flush! Constructed of non-corrosive materials that resist microbes & fungal growth. Anti-evaporation snap/airlock means the bag never needs refilling and prevents odors. Will not interfere with flush mechanics.