Korky vs Fluidmaster: Which Toilet Repair Brand Is Better?

Walk into any Home Depot, Lowe's, or Ace Hardware and you will find two brands occupying the toilet repair aisle: Korky and Fluidmaster. Both are American companies with decades of manufacturing experience, both supply parts compatible with nearly every major toilet brand, and both retail at accessible price points. Yet they have distinct engineering philosophies, material choices, and product strengths that make one a better fit depending on what part you need to replace.

This comparison covers fill valves, flappers, flush valves, complete tank repair kits, and specialty products from both brands. It draws on published specifications, owner reviews aggregated across thousands of verified purchases, and compatibility data for toilets from TOTO, Kohler, American Standard, Woodbridge, Swiss Madison, and Gerber. Whether you are fixing a running toilet, a ghost flushing problem, or planning a full tank overhaul, this guide gives you a clear answer.

For a broader look at toilet quality from the factory, see our guide to the best flushing toilets available today. And if you are troubleshooting an existing toilet, our guides on fixing a running toilet, choosing the right flapper, and fill valve replacement cover those topics in depth.

Fluidmaster's 400A fill valve, introduced decades ago, became the industry standard largely because it replaced the old ballcock design with a simpler, quieter, and more reliable float-cup mechanism. Today Fluidmaster claims its products are used in more than 100 million toilets worldwide. The company holds patents on anti-siphon mechanisms, adjustable fill valves, and the push-button dual-flush systems used in several imported toilet brands.

Korky's defining innovation is its proprietary rubber chemistry. The company produces its own rubber compounds at its Wisconsin facility, which allows it to optimize flappers for specific water conditions. This matters because most municipal water systems in the United States now use chloramines rather than chlorine as a disinfectant. Chloramines degrade conventional rubber flappers significantly faster than chlorine, causing premature hardening, warping, and seal failure. Korky's chloramine-resistant formulations directly address this problem, and the company is transparent about its water compatibility claims in published product documentation.

It is worth noting that neither company manufactures the toilet itself. Their parts are designed as universal repairs or replacements for internals across virtually every major toilet brand. TOTO Drake and Drake II tanks accept standard 2-inch flappers that both brands make. Kohler Highline and Cimarron tanks use 3-inch flappers, a category where Korky's 3-inch high-performance flapper has fewer direct competitors. American Standard Champion 4 and Cadet 3 models are also widely supported by both brands, though American Standard's 3-inch flush valve seat may require specific part numbers to ensure a leak-free seal.

Fill valves control water entry into the tank after a flush. When they fail, the toilet either runs continuously, fills too slowly, or fails to shut off, wasting hundreds of gallons per day. Both brands offer multiple fill valve lines, but their flagship products define each company's approach.

Fluidmaster Fill Valves

The Fluidmaster 400A is the benchmark. It installs in under 10 minutes, adjusts from 7 to 13 inches to fit most tank configurations, and is compatible with every major toilet brand. The 400AH adds an anti-siphon feature for areas with code requirements. The 400CR is the chloramine-resistant version with a reinforced seal. The 400ARHR (Tall) handles toilets with deep tanks, including some Woodbridge models.

Above the 400 series, Fluidmaster offers the 400LS (leak sentry), which automatically shuts the water off if the fill valve detects a leak, and the 400CRP14 Complete Repair Kit, which includes fill valve, flapper, and refill tube as a single replacement package. For toilets with older connections, Fluidmaster also makes ballcock replacement adapters.

Korky Fill Valves

Korky's QuietFILL Platinum fill valve is the direct competitor to the 400A. Its defining feature is a sealed tower design that Korky says prevents float-related overflows. User reviews consistently note that it operates more quietly than the standard 400A, particularly during the refill phase, though the 400AH and Fluidmaster's quieter line close that gap. The Korky fill valve also uses the brand's proprietary rubber compounds in its seals, which extends service life in chloramine environments.

Korky's 528MP MasterPlunger series takes a different approach, bundling fill valve replacement with a sealed cup float that is less prone to waterlogging than open-float designs. The 528 line fits most 2-inch valve configurations and is compatible with TOTO, Kohler, American Standard, and Gerber toilets.

The flapper is the rubber seal inside your tank that opens to allow water to rush into the bowl during a flush and then closes to allow refilling. When it fails, your toilet runs constantly, wasting an average of 200 gallons per day according to the EPA. Flappers are the single most common toilet repair in U.S. homes.

Flapper Sizes and Compatibility

Flappers come in two standard sizes for residential toilets: 2-inch and 3-inch. The size refers to the drain opening (flush valve seat) diameter, not the flapper body itself. Matching the correct size is critical. A 2-inch flapper on a 3-inch valve seat will not seal properly and the toilet will run continuously. Common examples:

• TOTO Drake, Drake II, UltraMax II, Aquia IV: 3-inch flush valve
• Kohler Highline, Cimarron, Archer: 3-inch flush valve (uses Kohler-specific seat geometry)
• American Standard Champion 4: 4-inch flush valve (requires Champion 4 specific flapper)
• American Standard Cadet 3: 3-inch flush valve
• Woodbridge T-0001: 3-inch flush valve
• Gerber Maxwell, Gerber Viper: 2-inch or 3-inch depending on model year
• Swiss Madison Clarence, Ivy: 3-inch flush valve
• Older gravity toilets (pre-1994): typically 2-inch

Korky Flappers: Product Lineup

Korky's bestselling flappers are the TORK series (universal 2-inch and 3-inch), the Perform series (chloramine-resistant premium), and the dedicated Champion 4 replacement (part 4010BP) for American Standard's large-bore valve. The Perform flapper uses Korky's highest-grade rubber compound and carries a claimed 10-year service life in lab testing, though real-world service life depends heavily on local water quality and UV exposure from tank lid removal.

Korky also makes a Kohler-specific 3-inch flapper designed to match Kohler's canister valve seat geometry, which differs slightly from generic 3-inch designs. Without the correct seat interface, even a quality 3-inch flapper may rock or fail to seal against Kohler flush valves, causing a slow leak that is hard to diagnose.

Fluidmaster Flappers: Product Lineup

Fluidmaster's PerforMAX line (part 502P series) uses a wider-than-standard seal surface to compensate for warped or worn flush valve seats. This is a practical advantage for older toilets where the seat has developed grooves or mineral deposits over time. Fluidmaster also makes the 5403 adjustable flapper, which allows homeowners to vary the flush volume from a standard 1.6 GPF tank without replacing the entire flush valve. This is one of Fluidmaster's most distinctive flapper products with no direct equivalent from Korky.

Complete repair kits save time and money compared to buying parts separately. They also ensure parts compatibility, since a fill valve and flapper from the same manufacturer are tested to work together. Both brands offer kits at the $15 to $30 range at major retailers, making them the most economical approach to a full tank rebuild.

Fluidmaster 400CRP14

The 400CRP14 includes the 400A fill valve, a PerforMAX flapper, and a refill tube. It is the most widely stocked repair kit at U.S. retailers. Installation instructions are clear, the parts are color-coded for quick identification, and the fill valve adjusts without tools. The chloramine-resistant version (400ARHR kit) adds the 400CR fill valve for an additional cost. This kit is compatible with most two-piece toilets from Kohler, American Standard, Gerber, and older Woodbridge models.

Korky 4010PK Complete Kit

Korky's complete kit pairs the QuietFILL Platinum fill valve with the chloramine-resistant Perform flapper and a refill clip. The QuietFILL's quieter operation during tank refill is a genuine differentiator, particularly in bathrooms adjacent to sleeping areas. For households in cities like Chicago, Seattle, Los Angeles, and New York, all of which use chloramine treatment, the Korky bundle's built-in resistance to water chemistry is a practical long-term advantage.

Compatibility is the most practical concern for anyone buying toilet repair parts. Manufacturers like TOTO and Kohler design their flush valves around standard geometries at the entry and mid-range levels, but premium and newer models increasingly use proprietary mechanisms.

TOTO Toilet Compatibility

TOTO Drake (both original and Drake II) and UltraMax II use a standard 3-inch flush valve seat. Both Korky's 3-inch TORK flapper and Fluidmaster's PerforMAX 3-inch seat correctly. The TOTO Aquia IV, a dual-flush model, uses a tower-style flush valve that is more proprietary. TOTO recommends OEM replacement parts for the Aquia IV's flush tower, and neither Korky nor Fluidmaster publishes a direct replacement for this component. For fill valves, both brands' adjustable models are compatible with TOTO tanks as long as height is set correctly.

Kohler Toilet Compatibility

Kohler Highline and Cimarron models produced before approximately 2010 use a standard 3-inch canister-style valve where aftermarket flappers fit acceptably. Kohler models produced after 2012 increasingly use a proprietary canister that Kohler states requires genuine Kohler GP84995 flappers. Korky's dedicated Kohler flapper (part 3070PN) is designed for older non-canister Kohler valve seats. Fluidmaster publishes less specific Kohler compatibility data. For fill valves, both brands' universal models fit Kohler tanks without modification.

American Standard Compatibility

American Standard Champion 4 uses a proprietary 4-inch flush valve. Korky part 4010BP is a purpose-built Champion 4 replacement that matches the seat geometry. Fluidmaster part 5407 also fits. American Standard Cadet 3 uses a more standard 3-inch valve, and both brands' universal 3-inch flappers perform well. The American Standard Vormax uses a proprietary EverClean flush system and requires OEM parts.

Woodbridge and Swiss Madison Compatibility

Woodbridge T-0001 and similar models use standard 3-inch flush valves compatible with universal flappers from both brands. Swiss Madison Clarence and Ivy models vary by production year, and compatibility should be confirmed by measuring the flush valve opening before purchase. Gerber toilets, including the Maxwell and Viper lines, use standard 2-inch or 3-inch seats depending on model, and both brands publish Gerber compatibility.

EPA WaterSense certification requires that a complete toilet flush at 1.28 gallons per flush or less while achieving a minimum MaP score of 350 grams per flush. The certification applies to the entire toilet unit, not to individual repair parts. However, the condition of internal tank components directly affects whether a toilet achieves its rated GPF.

A leaking or worn flapper can cause a toilet to consume far more water than its rated GPF because water slowly seeps into the bowl and triggers additional fill cycles. EPA estimates that a leaking flapper wastes 200 or more gallons per day. Replacing a failing flapper with a quality component from either Korky or Fluidmaster restores the toilet to its design efficiency, which for WaterSense-certified toilets like the TOTO Drake II or American Standard H2Option means returning to 1.28 GPF or dual-flush performance.

Fluidmaster's dual-flush conversion kit (part 400-075) is particularly relevant here. This product converts single-flush 1.6 GPF toilets to dual-flush operation with a 0.8 GPF liquid-waste cycle and a 1.6 GPF solid-waste cycle, substantially reducing annual water use. This is a category where Fluidmaster has a genuine advantage over Korky, which does not offer a comparable retrofit conversion product.

Aggregated owner reviews across major retailers show both brands scoring 4.3 to 4.7 out of 5 stars on flagship fill valve products. Differences emerge in specific failure modes. Fluidmaster 400A complaints most often cite noise (hissing during refill at higher water pressures), plastic float arm cracking over time, and occasional installation issues with older ballcock shanks. Korky fill valve complaints most often cite difficulty with height adjustment on certain configurations and occasional incompatibility with deep or unusually shaped tanks.

For flappers, Korky's rubber formulations consistently earn higher durability ratings in areas with chloramine water treatment. Reviewers in major U.S. cities with chloramine water frequently note Fluidmaster flappers lasting 1 to 2 years before showing signs of degradation, while Korky's Perform flappers in the same locations show notably longer service intervals before requiring replacement. In areas with older chlorine-only water treatment (common in rural and suburban systems), the durability gap narrows considerably.

Both brands maintain responsive customer service and honor warranty replacements without requiring the original receipt in most cases, which is an important practical consideration for parts that may fail years after purchase.

Both brands design their products for DIY installation without specialized tools. A standard fill valve replacement requires turning off the supply valve, flushing the tank to empty it, disconnecting the supply line, removing the old fill valve's mounting nut, inserting the new valve, reconnecting the supply line, and adjusting the water level. Most homeowners complete this in under 15 minutes following either brand's included instructions.

Fluidmaster's 400A height adjustment is generally cited as simpler in owner reviews. The clip-lock adjustment mechanism lets you set the height by squeezing a clip and rotating the top section. Korky's fill valve uses a twist-lock adjustment that some users find less intuitive on initial installation but equally secure once set correctly.

For flappers, both brands use standard mounting ears that attach to the overflow tube pegs, plus a refill tube or chain connection to the flush handle arm. The chain length matters more than brand in flapper installation. A chain that is too short prevents full flapper opening and reduces flush power. A chain that is too long can catch under the flapper and cause it to remain open, running the toilet continuously.

Korky's dedicated toilet-specific flappers (like the Kohler and Champion 4 versions) reduce the guesswork because they are engineered with the correct seat interface geometry, rather than relying on a universal adjustment mechanism. For first-time DIYers unfamiliar with flush valve geometry, the toilet-specific Korky parts reduce the risk of buying the wrong universal part.

Choose Fluidmaster when:

• You are replacing the fill valve and want the most universally compatible option
• You want a dual-flush conversion kit for an existing 1.6 GPF toilet
• You want an adjustable flapper to reduce flush volume without replacing the toilet
• You are rebuilding a tank and want the most widely available parts
• Your water supply uses chlorine (not chloramine) treatment
• You want a complete repair kit from the most widely stocked brand

Choose Korky when:

• You are replacing a flapper in a city with chloramine water treatment
• You need a toilet-specific flapper for Kohler Highline, Cimarron, or American Standard Champion 4
• You want a quieter fill valve for a bathroom near sleeping areas
• Your flappers have been failing faster than expected (sign of chloramine water)
• You want a complete kit with chloramine-resistant rubber throughout
• You are repairing a TOTO Drake, Drake II, or UltraMax II with a 3-inch flush valve

Use both brands together:

The most pragmatic approach, widely used by experienced plumbers, is to pair Fluidmaster fill valves with Korky flappers. This hybrid approach captures each brand's best product category. Fluidmaster's 400A fill valve is genuinely hard to beat for reliability, universal fit, and ease of installation. Korky's flappers offer superior durability in modern water systems. Both brands' parts are mechanically compatible in the same tank without any conflict.

• EPA WaterSense, epa.gov/watersense
• MaP flush testing, map-testing.com
• Manufacturer published specifications
• Fluidmaster product documentation and compatibility charts, fluidmaster.com
• Korky product documentation and compatibility charts, korky.com
• EPA Safe Drinking Water information, epa.gov/sdwa
• Aggregated owner reviews from major U.S. hardware retailers
• TOTO USA product specifications, us.totousa.com
• Kohler plumbing product documentation, kohler.com
• American Standard product specifications, americanstandard-us.com

• How to Fix a Running Toilet: Step-by-Step Diagnosis and Repair
• Toilet Flapper Guide: Sizes, Types, and When to Replace
• Toilet Fill Valve Guide: How They Work and How to Replace Them
• Best Toilet Repair Kits: Complete Tank Rebuild Options
• Best Flushing Toilets: Top Picks Ranked by MaP Score and Value