The Tank Bank is the easiest device to use to save water - fill to top, snap to close and hang in toilet tank .Worry-free water savings for the lifetime of the toilet. Constructed of non-corrosive materials that resist microbes and fungal growth.* Easy-to-fill* Patented air lock and fill valve - no water evaporation which means the bag never needs refilling* Every flush saves water - up to 0.8 gallons per flush!* Maintenance-free