Aqua Plumb C5621 Flapper For Toto Power Gravity. 3" oversize, replaces THU140S. This flapper is made out of chlorine chemical resistant, and a stainless steel hook & chain. To install, turn water supply off. flush toilet to drain tank, and sponge dry. Next remove the worn flapper from lugs on overflow tube. Remove the chain from flush lever arm, and attach the new flapper to lugs on overflow tube. Fasten the chain onto the flush lever arm with hook. Adjust the chain to minimize slack when the flapper is in the closed position. Turn on the water supply and fill the tank.