How to Replace a Toilet Flapper
Updated February 20, 2026
Stop a running toilet by replacing the flapper -- the $5 rubber seal at the bottom of the tank. 10-minute fix that saves hundreds of gallons per day.
Overview
The flapper is a rubber seal that lifts when you flush and drops back to seal the tank. When it wears out, water seeps into the bowl constantly -- a running toilet that wastes 200+ gallons per day. Replacing it is the easiest plumbing repair there is. No tools required. Unhook the old one, hook on the new one, adjust the chain. Five minutes. The only catch: not all flappers are universal. Take the old one to the store to match size, or know your toilet brand and model.
What You'll Need
Safety First
- Turn off the water supply before removing the old flapper to prevent the tank from refilling while you work.
- Tank water is clean (it has not entered the bowl), but wear gloves if the inside of the tank is slimy from mineral or algae buildup.
Step-by-Step Instructions
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Turn Off Water and Flush
Turn off the water supply at the shut-off valve behind the toilet (clockwise). Flush the toilet and hold the handle down to drain as much water as possible. The tank does not need to be completely empty, but less water makes the job cleaner.
Tip: If the shut-off valve is stuck or does not fully close, turn off the main water supply. This is also a good time to note that the valve needs replacing. -
Remove the Old Flapper
Reach into the tank and unhook the flapper from the two ears (pegs) on the overflow tube. Disconnect the chain from the flush lever arm. Pull the flapper out. Inspect it -- if it is warped, stiff, cracked, or has mineral buildup, it needed replacing. If it is soft and floppy, the flush valve seat may also need attention.
Tip: Take the old flapper to the hardware store. Matching by sight is the most reliable method. If you know the toilet brand and model (stamped inside the tank or on the bowl), you can also look up the correct part number. -
Clean the Flush Valve Seat
While the flapper is off, run your finger around the flush valve seat (the ring the flapper seals against). If it feels rough, gritty, or has mineral deposits, the new flapper will not seal properly. Clean it with fine emery cloth or a Scotch-Brite pad. Wipe clean with a rag. The surface should feel smooth.
Tip: If the seat is deeply pitted or corroded, a seat repair kit ($5-8) installs a smooth silicone ring over the damaged surface. Faster and cheaper than replacing the entire flush valve. -
Install the New Flapper
Hook the new flapper's ears onto the pegs on the overflow tube. Connect the chain to the flush lever arm. Adjust the chain so there is about 1/2 inch of slack when the flapper is closed. Too much slack: the flapper will not lift fully when you flush (weak flush). Too little slack: the chain holds the flapper slightly open (running toilet).
Tip: Some flappers have an adjustable dial or float that controls how long they stay open. Set it to the middle position first, then adjust if the flush is too weak (increase open time) or wastes water (decrease). -
Turn On Water and Test
Turn the water supply back on. Let the tank fill. Flush two or three times and watch the flapper operation -- it should lift fully, stay open until the tank is mostly empty, then drop and seal. Listen: the fill valve should shut off within 60 seconds and there should be no sound of running water afterward. Do the dye test: add food coloring to the tank, wait 15 minutes without flushing. No color in the bowl? Seal is good.
Tip: If the toilet still runs after replacing the flapper, the fill valve may also be faulty. Check the water level -- if it is rising above the overflow tube, the float or fill valve needs adjustment.
Pro Tips
- Replace the flapper every 3-5 years as preventive maintenance, even if it seems to be working. Rubber deteriorates gradually and a slow leak wastes water before you notice it.
- Avoid drop-in tank cleaning tablets with bleach or harsh chemicals. They accelerate flapper deterioration dramatically. Clean the bowl instead.
- Korky and Fluidmaster are the two most common aftermarket flapper brands. Both make universal models that fit most toilets, plus brand-specific models for Kohler, American Standard, and TOTO.
- If the chain keeps getting caught under the flapper (causes running), trim the excess chain with wire cutters or clip it to the lever arm to keep it out of the way.
- A running toilet can waste 200+ gallons per day. That is $50-100+ per month on your water bill. A $5 flapper pays for itself in a single day.
When to Call a Pro
Replacing a flapper is always DIY. But if the toilet still runs after a new flapper and a clean seat, the flush valve may need full replacement (a bigger job involving removing the tank). If you are uncomfortable working inside the tank or the shut-off valve will not close, a plumber can handle the whole job quickly.