If you've tried a new flapper to fix your running toilet and it still runs don’t give up hope. Here's a fix that's sure to work.
Follow the directions included with your flush seat repair kit to seal a new repair seat onto the old, damaged seat.
If you hear your toilet refilling too often, or if you hear the steady hiss of running water, the flapper may be leaking. The flapper (aka “flush valve seal”) is the plug that falls against the drain hole (flush valve drain seat) on the bottom of the tank and holds water in until the next time you flush. When flappers or flush valve seats wear out, water trickles out, causing the water valve to open to refill the tank. Usually the fix is simple. Remove the old flapper and take it with you to the hardware store or home center to find a matching replacement. Occasionally a new flapper doesn’t solve the problem. If you’ve tried replacing the flapper but the toilet still runs, the flush valve seat is probably rough or pitted. You can replace the entire flush valve, but it’s a big job. Here’s an easier fix. Look for a flapper kit that contains a flush seat repair. We show a Fluidmaster 555C kit ($7), but others are available. The kit contains a flapper and matching seat that you adhere to the damaged seat with the adhesive provided, as shown. Start by closing the valve on the water line to the toilet by turning it clockwise. Then flush the toilet and hold the flapper open to allow the water to drain from the tank. Use a sponge to mop out the water that remains. Follow the included instructions to install the new valve seat and flapper. The Fluidmaster flapper we show includes a plastic cup that allows you to adjust the length of time the flapper stays open. It’s for toilets that use 3.5 gallons or less for a flush. If your toilet uses more than this, remove the timing cup. Install the new flapper. Then adjust the length of the chain so it’s just slightly slack when the flapper is down. Turn on the water and test the flush. You may have to fiddle with the length of the chain to get the flapper working correctly. When you’re done, cut off the excess chain to keep it from getting stuck under the flapper.