Stop a running toilet

Lift the tank lid off and set it somewhere flat. Flush once and watch. Note whether water spills into the open overflow tube, or you hear a hiss at the flapper on the bottom while the tank keeps topping up.

If water spills into the overflow tube, lower the level. On a ball-and-arm float, bend the arm down slightly. On a cup-style fill valve, lower the cup or turn the screw so the valve shuts off about a finger-width below the top of the overflow tube.

If the hiss is at the bottom, turn the supply valve behind the toilet clockwise until it stops. Flush and hold the handle so the tank empties.

Give the chain a little slack and make sure it is not pinned under the flapper. The chain should lift the flapper and then let it drop flat.

Wipe the flapper seat with a sponge. If the rubber is warped, cracked, or stiff, fit a new flapper of the same size and hook the chain with that same small amount of slack.

Open the supply slowly. The filling should stop on its own. A few drops of food coloring in the tank will show in the bowl after ten minutes if the flapper is still leaking. Reseat it and test again.

Set the lid back on once the tank holds a steady level and stays quiet.