How to Replace a Toilet Flapper (Step-by-Step Guide)
How to replace a toilet flapper in 15 minutes for $5. Covers removing the old flapper, picking Korky or Fluidmaster, and setting the chain right.
Quick answer: To replace a toilet flapper, turn off the supply valve behind the toilet, flush to drain the tank, unhook the old flapper from the two pegs on the overflow tube, disconnect the chain from the lever, and snap the new one on in reverse order. The job takes 10 to 15 minutes. The only thing that bites people is sizing: most toilets built before 2000 take a 2-inch flapper; newer and high-efficiency models often take a 3-inch. Korky and Fluidmaster are the two brands worth buying. Cost: $5 to $10 for the part.
A worn flapper is the cause of a running toilet about 80% of the time. The EPA WaterSense program puts a running toilet at up to 200 gallons of water wasted per day, which runs $20 to $70 extra on a monthly water bill depending on local rates. The fix is a $5 rubber disc and fifteen minutes.
Flappers require no special tools, no main water shutoff, and no plumbing experience. If you’ve replaced a light switch or a doorknob, you can do this.
What You’ll Need
- Replacement flapper ($5-10, see Step 3 on sizing before buying)
- Rubber or latex gloves (optional: tank water is clean, but it’s still tank water)
- Old towel or sponge (for residual tank water)
- Adjustable wrench (only needed if the supply valve is stuck)
One note: don’t buy the flapper before you pull the old one out. Take the old flapper to the hardware store and match it. Universal flappers are often close enough to leak again within a year.
Step 1: Shut Off the Water and Drain the Tank
Find the supply valve behind the toilet near the floor. It’s a small oval knob. Turn it clockwise until it stops, snug but not torqued down.
Flush the toilet. Most of the water drains in one flush. If some remains, a sponge or old towel handles it. You’re not operating in a sterile environment here; an inch of water at the bottom of the tank is fine to work around.
Lift the tank lid and set it on a folded bath towel on the floor. Porcelain lids are heavier than they look and crack on tile without warning.
Step 2: Remove the Old Flapper
The flapper sits over the large hole at the bottom of the tank. It connects in two places.
The ears. Most standard flappers have two rubber ears that hook onto small pegs on either side of the overflow tube (the tall center pipe in the tank). Pinch or unhook each ear in turn. Some older toilets use a ring-style mount where the flapper slides over the overflow tube instead of clipping onto pegs. If yours does, slide it upward.
The chain. Unhook the chain from the flush lever arm. The clip usually pops off a hole in the arm. Note which hole in the lever the chain was attached to before you disconnect it.
Set the old flapper aside in a paper towel. If you’re not sure about sizing, take this to the hardware store.
Step 3: Pick the Right Replacement Flapper
Two things to match: size and mount type.
Most toilets built before around 2000 use a 2-inch flush valve seat. Most toilets built after 2000, especially elongated and high-efficiency models, use a 3-inch seat. With the flapper off you can see the difference easily: the 2-inch opening looks about the size of a golf ball; the 3-inch looks closer to a baseball. A tape measure across the seat opening settles it definitively.
Some manufacturers, Kohler and American Standard in particular, use proprietary flapper geometries on their mid-range and higher models. If you bought a name-brand toilet in the last 15 years, check the model number on the inside of the tank lid before shopping. Fluidmaster’s website has a compatibility lookup by model number if you want to confirm before buying.
Two brands worth buying:
- Korky (about $5-7): their universal 2-inch and 3-inch flappers fit most toilets, reliable rubber quality
- Fluidmaster 502 (about $6-9): their workhorse replacement flapper; also comes in adjustable-flow versions for water conservation on older high-volume toilets
Both Korky and Fluidmaster rate their standard flappers at 5 to 7 years in normal water. If you’ve been using blue chlorine drop-in tank tablets, figure 1 to 2 years. The chlorine degrades the rubber significantly faster. Those tablets are an efficient way to end up buying flappers every eighteen months.
For mount type: if the old flapper used the two-ear clip design, buy a two-ear replacement. If it used a ring-style mount, match the ring. These are usually not interchangeable.
Step 4: Install the New Flapper
Hook both ears onto the overflow tube pegs. They should snap on with light pressure. The flapper needs to sit flat and centered over the flush valve seat. Lift it and let it drop a few times to confirm it closes flat with no off-center tilt.
If yours is a ring-style mount, slide the ring down over the overflow tube until it sits against the flush valve seat.
Don’t force it. If a flapper won’t seat flat, it’s either the wrong size or the wrong type. A flapper that’s even slightly off-center will run.
Step 5: Set the Chain and Test the Flush
Reconnect the chain to the flush lever arm. This step matters more than people expect.
Too short: the chain holds the flapper slightly open and the toilet runs continuously after every flush. Too long: the chain gets pinched under the flapper as it closes. Same result.
The right length is about a half inch of slack when the flapper is fully seated. Hold the chain taut between the flapper and the lever arm, then give it one extra link of slack. Clip it there.
Turn the water back on. Listen as the tank fills. When it reaches the waterline (about an inch below the top of the overflow tube), the fill valve should go quiet. If the fill valve runs indefinitely after the tank is full, that’s a fill valve issue, not a flapper issue. See why a toilet won’t stop filling up.
Flush twice and watch the flapper drop and seal cleanly each time. If you still hear water running into the bowl after the tank refills completely, press down on the flapper with one finger. If the sound stops when you apply pressure, the flapper isn’t sealing against the seat. Usually that means the seat itself has corrosion or pitting that a new flapper can’t fix. You’ll need a seat repair kit ($3-5) or a new flush valve.
Put the tank lid back on only after confirming the flush works correctly. Skip the test and you’re pulling the lid off again in five minutes. A fifteen-minute job becomes forty-five.
Common Mistakes
Buying before sizing. Two toilets of the same age in the same house can take different flapper sizes. Pull the old one first, then shop. Bring it in a paper towel if you want to be certain.
Chain too long. A long chain feels like the safe choice. In practice it coils under the flapper as the tank refills and breaks the seal. If the toilet runs and you press down on the flapper and it stops, check the chain length before assuming you need another part.
Skipping the post-install test. The lid goes on last. Flush twice and confirm everything is working before you put it back. Sixty seconds of observation now saves you pulling the lid off again.
Using drop-in tank tablets. Blue chlorine tablets clean the bowl but accelerate rubber degradation. If you’ve been using them and you’re on your second flapper in two or three years, the tablets are why. Switch to an in-bowl rim block instead. Same cleaning effect, no contact with tank components.
Ignoring a pitted seat. A new flapper won’t seal against a corroded flush valve seat. If you replaced the flapper and the toilet still runs, do the finger test. If pressing down on the flapper stops the running, the seat is the issue, not the flapper. A seat repair kit handles minor corrosion; a flush valve replacement handles worse cases. The toilet repair guide covers the full diagnosis.
FAQ
How do I know my flapper needs replacing?
The clearest sign is a toilet that runs intermittently between flushes. You’ll hear the fill valve kick on every hour or so to top off the tank. A more definitive test: drop a few drops of food coloring into the tank and wait 20 minutes without flushing. If color shows up in the bowl, the flapper is leaking. Korky and Fluidmaster both recommend replacing flappers every 3 to 5 years as preventive maintenance regardless of symptoms, since the rubber degrades even when it looks intact.
Can I replace the flapper without turning off the water?
You can remove the flapper while the water is on, but turning off the supply valve takes five seconds and keeps the tank from refilling while you’re working. The shutoff is the small knob behind the toilet near the floor, not the main water supply for the whole house. If that valve is seized or corroded, shutting off water to the house covers the main shutoff location.
What’s the difference between a 2-inch and 3-inch flapper?
The 2-inch fits the flush valve opening on most toilets built before 2000 and on some lower-volume models built after. The 3-inch fits newer high-efficiency and elongated toilets where the larger valve opening delivers a stronger flush. Measure the opening with a tape measure if you’re unsure, or take the old part to the store.
Why is my toilet still running after I replaced the flapper?
Three most common causes: the chain is too long and is getting pinched under the flapper, the flush valve seat is corroded and the flapper can’t seal against it, or the fill valve needs replacing separately. Press down on the flapper while the toilet is running. If the sound stops, the seat is the problem. If it doesn’t stop, the fill valve is the issue. For a complete diagnosis, the running toilet repair guide covers all three causes.
How long should a toilet flapper last?
In normal water, 5 to 7 years is typical for a Korky or Fluidmaster standard flapper. Hard water areas, which accelerate mineral buildup on the flush valve seat, tend to shorten that. Blue chlorine tank tablets cut it to 1 to 2 years. Replacing flappers every 3 to 5 years as preventive maintenance is a reasonable cadence for most households.
Should I replace the fill valve at the same time?
If the fill valve is more than 7 to 10 years old and the toilet has been having issues, yes. It’s an extra $12 and twenty minutes, and you’re already in the tank. A Fluidmaster 400A is the standard replacement. On a newer toilet where the fill valve is working correctly, just replace the flapper.
What if the flapper won’t clip onto the overflow tube pegs?
The flapper is either the wrong size or the wrong mount type. Ring-style flappers won’t clip onto peg mounts, and clip flappers won’t slide over a tube that needs a ring mount. Compare your old flapper to the replacement before installing. The ear and ring designs look noticeably different. If you’re on your third attempt with a “universal” flapper and it still won’t seat flat, take the old part to the hardware store and ask someone to match it by hand.
Can I replace the flapper on any toilet brand?
For most toilets, yes. American Standard, Kohler, TOTO, Glacier Bay, and most big-box brands accept aftermarket flappers from Korky or Fluidmaster in the right size. A subset of Kohler and American Standard models use proprietary seat geometries that don’t accept universal replacements. Check the model number on the inside of the tank lid if you have a mid-range or higher model from either brand.