A toilet flapper is a rubber seal that sits at the bottom of your tank and lets water flow into the bowl when you flush

When a flapper wears out or warps, water leaks slowly from the tank into the bowl — you'll notice the toilet running on its own or the water level dropping without anyone flushing. Replacing one takes about 15 minutes and costs $5 to $15 for the part itself. You don't need special tools, just a basic understanding of how your tank works and a willingness to get your hands wet.

The flapper is the most common reason a toilet runs constantly. It's also one of the easiest repairs you can do yourself. The process is the same whether your tank is old or new, though the exact shape of the flapper varies slightly by manufacturer.

Key Takeaways

  • A worn flapper is the most common cause of a running toilet and is visible inside the tank as a rubber disc or oval attached to a chain.
  • You can buy a replacement flapper at any hardware store or online for under $15, and most are universal or fit your specific toilet model.
  • The entire replacement takes 15 minutes and requires only turning off the water supply and unclipping the old flapper from its hinges.
  • If the flapper seat (the rim it seals against) is cracked or pitted, the new flapper won't seal properly and you'll need a plumber or a full tank replacement.

Turn off the water and empty the tank

Locate the shutoff valve on the water line behind or below your toilet. Turn it clockwise until it stops — you should feel resistance, not a hard stop. Flush the toilet to drain the tank completely. If water doesn't drain, the shutoff valve is broken and you should call a plumber before proceeding.

Once the tank is empty, wipe the inside dry with a towel or sponge. You don't need it bone-dry, but removing standing water makes it easier to see what you're doing and prevents splashing when you remove the old flapper.

Identify the flapper and its attachment points

Look inside the tank. The flapper is a rubber disc or oval-shaped piece sitting on top of a hollow tube called the flush valve at the bottom center of the tank. A chain or strap connects the flapper to a lever arm that extends up to the flush handle. The flapper is held in place by two small plastic or metal clips on either side of the flush valve.

Take a photo of how the chain attaches to the lever arm — the length of slack matters. Most flappers have a small hook at the end of the chain that clips into a hole on the lever. If yours uses a strap instead of a chain, note how it's positioned before you remove it.

Remove the old flapper

Unhook the chain or strap from the lever arm first. Then, gently lift the flapper straight up and off the two clips on the flush valve. It should come free with light pressure — if it's stuck, the rubber has likely hardened and fused to the valve seat, which is a sign it's definitely time to replace it.

Inspect the flush valve seat (the rim the flapper sat on) for cracks, pitting, or mineral buildup. If you see white or tan crusty deposits, you can clean them with a damp cloth or soft brush. If the seat itself is cracked or has a rough, pitted surface, a new flapper won't seal properly and you'll need professional help.

Install the new flapper

Most flappers come with instructions specific to your toilet model. Read them first — some have slightly different clip configurations. Position the new flapper so the two clips on either side of the flush valve slide into the grooves or slots on the flapper. The flapper should sit flat and centered on the valve seat.

Reattach the chain to the lever arm. The chain should have about a quarter-inch of slack when the flapper is resting on the valve seat. Too much slack and the flapper won't seal; too little and the chain will hold the flapper slightly open, causing a leak. Adjust by moving the hook to a different hole on the lever arm if needed.

Test the repair and watch for leaks

Turn the shutoff valve counterclockwise to refill the tank. Listen for the fill valve to stop — this usually takes 30 seconds to a minute. Flush the toilet and watch the flapper close. It should seal when ready and the tank should stop refilling within a few seconds.

Let the toilet sit for 10 minutes without flushing. If the water level drops or you hear the fill valve running again, the flapper isn't sealing. Check that the chain has the right amount of slack and that the flapper is sitting flat on the valve seat. If it still leaks after adjustment, the valve seat may be damaged and you'll need a plumber.

Common flapper types and where to find them

Universal flappers fit most standard toilets made in the last 20 years. Kohler, American Standard, and Toto also make model-specific flappers if you want an exact match. You can find the model number on a sticker inside the tank or on the bowl itself.

Hardware stores stock flappers in the plumbing aisle near fill valves and tank bolts. Online retailers like Amazon carry dozens of options with next-day shipping. Bring a photo of your old flapper or the toilet model number if you're unsure which one to buy — most store staff can match it for you in seconds.

When to call a professional instead

If the flush valve seat is cracked, pitted, or severely corroded, a new flapper won't seal no matter how well you install it. A plumber can replace the flush valve itself, which involves draining the tank and removing bolts — a job that takes an hour or two and costs $150 to $300 depending on your location.

If the shutoff valve won't turn or leaks when you try to use it, don't force it. A stuck or broken shutoff valve is a plumber's job and should be fixed before you attempt any tank work. If you're uncomfortable working inside the tank or the flapper doesn't stop the leak after you've adjusted the chain, a plumber can diagnose the real problem quickly.

Frequently Asked Questions

How do I know if my flapper is actually the problem?

Put food coloring in the tank and wait 10 minutes without flushing. If the color moves into the bowl, water is leaking past the flapper. If the color stays in the tank but you hear the fill valve running, the flapper is letting water escape. A running toilet almost always means a worn flapper.

Can I clean the old flapper instead of replacing it?

You can try soaking it in white vinegar for an hour to dissolve mineral deposits, but rubber that's hardened or warped won't soften. Most flappers last 4 to 7 years before the rubber degrades. Replacement is cheaper and faster than troubleshooting a cleaning attempt.

What if the chain is too long or too short after I install the new flapper?

Adjust the chain by moving the hook to a different hole on the lever arm — most arms have 3 to 5 holes. If the chain is still wrong, you can also tie a knot in it to shorten it, though this looks rough. A quarter-inch of slack is the target when the flapper rests on the valve seat.

Do I need to turn off the water before I start?

Yes. Even though the tank is above the flapper, turning off the water prevents the tank from refilling while you work and gives you time to inspect the valve seat without water running. It takes 10 seconds and prevents mistakes.

Will replacing the flapper fix a slow leak under the toilet?

No. A slow leak under the toilet usually means the tank bolts are loose or the rubber seals around them are cracked. That's a different repair. A leaking flapper causes water to run inside the tank, not pool under it.