Toilet Flapper Buying Guide: Size, Material, Brand

A toilet flapper is a roughly fist-sized rubber or silicone disc that seals the flush valve at the bottom of the tank. Every time you flush, it lifts, lets water rush into the bowl, then drops back down and reseals so the tank can refill. A worn or mismatched flapper is responsible for up to 200 gallons of wasted water per day per toilet, according to EPA WaterSense data, making it the single most common source of household water waste.

This guide covers every variable that determines the right flapper: seat diameter (2-inch vs. 3-inch), material (rubber, silicone, foam), adjustable vs. fixed flappers, brand and compatibility, and the fastest way to diagnose whether your flapper is actually the problem. We also cover how flappers interact with the broader flush system, so you understand why the wrong size or material will not merely shorten product life but will actively compromise flush power in top-ranked toilets like the best flushing toilets we cover across this site.

The toilet flapper seals the flush valve opening at the base of the tank. When you press the handle, it lifts via a chain, releasing a calibrated volume of water into the bowl to create flush momentum. After the tank empties, the flapper drops back onto its seat, creating a watertight seal that lets the tank refill without water continuously leaking into the bowl.

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TOTO Drake (CST744SL)

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TOTO Drake II (CST454CEFG)

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TOTO UltraMax II (MS604114CEFG)

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Woodbridge T-0001

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The flapper works in direct partnership with the flush valve seat -- the ring-shaped opening it rests against. If the flapper is too small, it will not seat properly and water will seep past the edges continuously. If it is too large, it may not seal flat and can rock slightly, creating an intermittent "phantom flush" or running toilet sound. The chain length also matters: too tight and the flapper cannot close fully; too long and it can get caught under the flapper, preventing a seal.

Because the flapper controls exactly how much water exits the tank during each flush, it directly affects gallon-per-flush (GPF) performance. An adjustable flapper lets you dial in the volume, which is particularly important in EPA WaterSense toilets rated at 1.28 GPF -- where the flush window is narrow and any air gap from a poorly seated flapper throws off the engineered water volume.

Size is the single most important variable in flapper selection. Install the wrong diameter and you will either get a constant slow leak (flapper too small, cannot bridge the opening) or poor sealing due to buckling or rocking (flapper too large for the seat ring). Here is a reliable way to determine which you need:

1. Lift the tank lid and locate the flush valve at the center bottom of the tank. The flapper sits directly over the circular opening.
2. Remove the old flapper by unclipping its ears from the overflow tube pegs and unhooking the chain from the flush handle arm.
3. Measure the flush valve seat diameter -- the ring the flapper seals against, not the overall flush valve body. A 2-inch seat measures roughly 2 inches across the interior opening; a 3-inch seat measures roughly 3 inches.
4. Cross-reference your toilet model number, printed on the inside of the tank near the waterline or on a sticker on the tank bottom. Enter it at the manufacturer's parts lookup or Fluidmaster's compatibility checker.

Note on dual-flush toilets: most modern dual-flush designs (TOTO Aquia IV, Swiss Madison Sublime II) use a tower-style flush valve with a canister seal, not a traditional rubber flapper. If you own one of these models, you are replacing a canister seal or tower gasket, not a flapper. The process and parts are different -- check our dual-flush toilet guide for those specifics.

Flapper material determines two things: longevity and how well the flapper seals against the valve seat surface. Here is a breakdown of the three main types:

Standard Rubber (Neoprene / EPDM)

The vast majority of flappers sold and installed are neoprene or EPDM (ethylene propylene diene monomer) rubber. They are inexpensive, widely compatible, and perform well when water chemistry is moderate. The limitation is chlorine and chloramine sensitivity: municipal water treatment in many US cities has shifted to chloramine, which is more aggressive to rubber than free chlorine. Rubber flappers in high-chloramine systems can degrade in as little as 18 months, producing a slimy residue and a progressively worse seal.

If you notice your toilet flapper turning sticky, slimy, or warping within two years of replacement, chloramine is almost certainly the cause. Water utilities are legally required to report chloramine use in their annual Consumer Confidence Reports -- check yours before selecting a material.

Silicone

Silicone flappers resist chlorine and chloramine degradation significantly better than rubber. Fluidmaster's PerforMAX and Korky's WaterWISE QuietFILL flappers use silicone or silicone-blended compounds. Published testing by Fluidmaster shows silicone flappers maintaining dimensional stability after accelerated aging equivalent to 10 years of municipal water exposure, where comparable rubber samples showed measurable surface tack and dimensional change at the 3-year mark.

Silicone flappers typically cost more than standard rubber options, which is higher upfront but lower total cost over a 10-year window.

Foam-Core

Foam-core flappers (most notably the Korky 100BP and 481BP lines) use a closed-cell foam layer beneath a rubber face. The foam compresses slightly under water pressure, improving the seal on flush valve seats that have minor surface irregularities -- chipping, mineral deposits, or slight warping. They are a practical choice for older toilets with worn valve seats where a standard rigid rubber flapper no longer seals reliably. Foam-core flappers are not the best choice for heavily chlorinated water.

Adjustable flappers have a dial or slider that controls how quickly the flapper closes. A slower-closing flapper releases more water per flush; a faster-closing flapper releases less. This matters because the engineered flush in a 1.28 GPF toilet is calibrated around a specific volume. If your flapper closes too fast, not enough water enters the bowl and you may need multiple flushes. If it closes too slowly, you exceed the rated GPF and lose the water-efficiency benefit.

The Fluidmaster PerforMAX (502P21 series) is the most widely tested adjustable flapper on the market and compatible with the majority of 2-inch flush valves. It ships with a 10-position dial pre-set to a mid-range volume. For most users, the mid-range setting matches the original OEM behavior. If you are seeing incomplete flushes, dial toward the "more water" setting and test. If your toilet is consuming noticeably more water than its rated GPF (verifiable by a dye test and timing the tank refill), dial toward "less water."

Fixed flappers remain the right choice for older 1.6 GPF toilets where exact volume is less critical, and for anyone who prefers a simpler install with no calibration step.

A running toilet does not always sound like a roaring stream. Slow flapper leaks produce an intermittent trickle -- often just a brief hiss every 10 to 20 minutes as the water level drops slightly and the fill valve tops up the tank. Homeowners often mistake this for normal refill behavior. Prolonged patterns of brief fill cycles, however, are a clear sign the flapper is not holding a full seal.

The Dye Test Procedure

1. Remove the tank lid and place it safely aside.
2. Add several drops of food coloring or a toilet tank dye tablet (widely available at hardware stores) into the tank water. The water should turn clearly blue, red, or green.
3. Do not flush. Wait 15 minutes.
4. Check the bowl. If the bowl water shows any color, water is seeping past the flapper. Replace the flapper.
5. If the bowl water is clear after 15 minutes, the flapper seals correctly and the issue may be the fill valve, supply line, or another component.

The dye test catches leaks that do not audibly run. The EPA WaterSense program estimates that 20 to 30 percent of toilets in US homes have a running toilet at any given time, with the majority caused by degraded or mismatched flappers. Conducting a dye test once per year -- or immediately if your water bill increases unexpectedly -- is a sound maintenance practice.

For more context on how flush-system components interact, see our guide to toilet fill valves and our detailed review of how toilets work.

The flapper aftermarket is dominated by a handful of brands. Here is how they differ in practice:

Fluidmaster

Fluidmaster is the largest plumbing fill-valve and flapper manufacturer in North America and holds a dominant market position in the aftermarket repair segment. Their model 400A fill valve is the de facto standard; their flapper lineup is similarly ubiquitous. The Fluidmaster 5403 is the reference 3-inch adjustable flapper and comes packaged with many Kohler and American Standard toilet repair kits. The PerforMAX 502 series is their premium silicone adjustable line. Aggregated retail reviews across major plumbing supply channels show Fluidmaster flappers consistently achieving 4.4 to 4.7 out of 5 stars over thousands of reviews.

Korky (Lavelle Industries)

Korky is Fluidmaster's primary competitor in the universal flapper segment. Their foam-core designs (100BP, 481BP) are a top choice for older toilets with worn valve seats, and their QuietFILL Platinum flappers use a chloramine-resistant compound. Korky's compatibility guides are published openly on their website and are cross-referenced by model number, making it easy to confirm fit before purchase. Aggregated owner reviews rate Korky flappers at 4.3 to 4.6 out of 5 across major retail platforms.

TOTO OEM Flappers

TOTO toilets including the Drake, Drake II, UltraMax II, and Aquia IV use flush valve seats manufactured to specific tolerances optimized for TOTO's high-efficiency flushing systems. The TOTO THU008 and THU167 flappers are designed to maintain flush performance in these valves without requiring calibration. While universal flappers can work in TOTO toilets, plumbing professionals widely recommend OEM parts for TOTO to preserve MaP flush-test performance scores. The TOTO Drake II, for instance, achieves a MaP score of 1,000 grams (the maximum score) -- performance that depends on the calibrated water release the OEM flapper provides.

Kohler OEM

Kohler's AquaPiston flush valves (used in the Highline and Cimarron) use a canister-style mechanism rather than a traditional flapper. The canister lifts vertically on flush and drops back onto a seat ring, sealed by a rubber gasket. If your Kohler toilet is leaking, confirm whether it uses an AquaPiston canister or a conventional flush valve before purchasing a replacement. Kohler's parts catalog, available at their website, lists the correct part by model number.

American Standard OEM

American Standard Champion 4 and Cadet 3 toilets use 3-inch flush valves. American Standard sells direct-replacement flappers (part 7301147-0070A for the Champion 4 3-inch valve) that are engineered to deliver the full flush volume without the calibration step adjustable aftermarket flappers require. The Champion 4 earns a MaP score of 1,000 grams -- the maximum score -- and its flush performance is partly attributable to the precise flapper-to-valve interaction. See our full American Standard Champion 4 review for more on how the flush system works.

Gerber OEM

Gerber toilets including the Viper and Avalanche use a variety of flush valve sizes. Gerber's OEM flappers are sold under the Gerber Plumbing Fixtures brand and are cross-referenced by valve series in their published parts manual. Fluidmaster universal flappers typically fit Gerber 2-inch and 3-inch valves, but Gerber's tank-to-bowl profile on some elongated models creates a chain geometry where a slightly longer chain or a different chain anchor point is needed to prevent the chain from interfering with the flapper seal.

Note: Kohler AquaPiston and TOTO tower-style dual-flush valves use canister seals rather than traditional flappers. The replacement process and parts differ meaningfully from standard flapper replacement.

Replacing a toilet flapper requires no special tools and takes approximately 10 to 15 minutes. You do not need to turn off the water supply to the home -- only the toilet's local shutoff valve.

1. Turn off the toilet's water supply. The shutoff valve is typically on the wall or floor behind the toilet. Turn clockwise until it stops.
2. Flush the toilet to drain most of the water from the tank.
3. Remove the tank lid and set it safely aside on a padded surface (tank lids crack easily).
4. Unhook the flapper chain from the flush handle arm. Note which hole in the arm the chain is connected to -- you will reconnect the new chain to the same position to preserve the original chain length.
5. Unclip the flapper ears from the overflow tube pegs. The ears are the two side loops on the flapper that hook over the small pegs extending from the overflow tube on either side. Pull each ear outward and up to release.
6. Inspect the flush valve seat -- the ring the old flapper sealed against. Run a finger around the surface. If you feel nicks, mineral buildup, or rough patches, use a fine emery cloth or toilet valve seat repair kit to smooth the surface before installing the new flapper. A new flapper on a damaged seat will not seal reliably.
7. Install the new flapper by clipping its ears onto the overflow tube pegs. The flapper body should rest flat over the flush valve opening with equal overlap on all sides.
8. Reconnect the chain to the flush arm at the same hole used previously. With the flapper seated, the chain should have approximately 1/2 inch of slack -- enough to lift freely when the handle is pressed, but not so much that it can fold under the flapper.
9. Turn the water supply back on. Allow the tank to fill completely.
10. Test the flush two to three times and watch that the flapper drops cleanly after each flush. Then perform a dye test to confirm the seal.

If the toilet continues to run after flapper replacement, the issue is likely the fill valve, the float adjustment, or a damaged flush valve seat. Consult our running toilet diagnosis guide for a systematic troubleshooting approach.

EPA WaterSense certification applies to the complete toilet, not to individual flappers. However, the flapper is integral to whether a WaterSense toilet actually achieves its certified 1.28 GPF rating in field conditions. An oversized or slow-closing flapper in a WaterSense toilet can push the effective GPF above the certified limit on every flush, negating the water-saving benefit. An undersized or fast-closing flapper reduces flush water volume below what the bowl needs, causing incomplete flushes and -- ironically -- requiring double-flushes that consume more water than a single 1.6 GPF flush.

MaP (Maximum Performance) testing evaluates toilet flush effectiveness using a standardized media (soybean paste and toilet paper) in grams. MaP scores above 500 grams are considered adequate; scores of 800 grams or above are considered excellent; the maximum score is 1,000 grams. These scores are established with the OEM flapper in place and calibrated water volume. Aftermarket flappers that change the effective flush volume will alter the real-world MaP performance even if the toilet's published score remains unchanged.

If you own an EPA WaterSense toilet and are replacing the flapper, the safest path to maintaining both water efficiency and flush performance is:

1. Use an OEM flapper when the toilet manufacturer offers one for your model.
2. If using an aftermarket adjustable flapper (Fluidmaster PerforMAX recommended), start at the mid-position and test flush quality and tank fill cycle duration before finalizing the adjustment.
3. Avoid fixed-volume aftermarket flappers with no adjustment on 1.28 GPF WaterSense toilets unless the brand explicitly states compatibility with your toilet model number.

• EPA WaterSense, epa.gov/watersense
• MaP flush testing, map-testing.com
• Manufacturer published specifications
• Alliance for Water Efficiency, allianceforwaterefficiency.org
• Fluidmaster product documentation and compatibility guides, fluidmaster.com
• Korky (Lavelle Industries) compatibility charts, korky.com
• American Standard parts catalog, americanstandard-us.com
• TOTO USA parts documentation, totousa.com
• Kohler plumbing parts reference, kohler.com
• American Society of Plumbing Engineers (ASPE) technical references, aspe.org

• Best Flushing Toilets: Top-Ranked Models by MaP Score
• Toilet Fill Valve Buying Guide: Types, Brands, Replacement
• Dual-Flush Toilet Guide: How They Work and Whether They Save Water
• Running Toilet Diagnosis Guide: Flapper, Fill Valve, or Float?
• American Standard Champion 4 Review: MaP Score, Flush Power, Verdict