Korky Vs. Fluidmaster: Which Fill Valve Is Better?

If you are reading this, you are likely suffering from the “phantom flush”—that ghostly sound of your toilet running in the middle of the night—or a hiss that just won’t quit. I have been there, staring at the porcelain throne at 2 AM, wondering if I need a plumber or just a $12 part. This led me to the two heavyweights of the toilet tank world: Korky and Fluidmaster.

Both brands promise to fix running toilets and fill the tank faster, but is there actually a difference? I installed the Korky QuietFill Platinum in my guest bath and the Fluidmaster 400A in my master bath to find out. I wanted to see if Korky really is quieter and if Fluidmaster truly deserves its reputation as the “universal” standard. This article details my real-world testing to help you pick the right valve to silence your bathroom.

A Brief Comparison Table

My Experience With Korky

I decided to try the Korky QuietFill Platinum (the silver cap version) specifically because my guest bathroom is right next to the living room, and the old ballcock valve sounded like a jet engine taking off.

Installation was surprisingly distinct from what I was used to.

Korky uses an internal float design, meaning there is no big black ball or cup floating up and down on the side; everything is contained inside the central column.

Fitting it into the tank was a breeze. Because it lacks that external float arm, it has a smaller footprint.

I didn’t have to worry about the float rubbing against the side of the tank or getting tangling with the flush lever chain.

The height adjustment involves twisting the body to unlock it, sliding it up, and twisting it back to lock.

I admit, I didn’t twist it hard enough the first time, and it slid down when the water pressure hit it.

Once I really cranked it into the “locked” position, it held firm.

The silence was the real shocker. When I turned the water back on, I actually thought it wasn’t working because I couldn’t hear the usual aggressive hiss. It fills the tank with a smooth, muted flow. If you are sensitive to noise, the marketing isn’t lying—it is noticeably quieter.

Pros Of Korky

• Superior Noise Control: Korky really earns the “QuietFill” name. By directing the water flow through a specially designed internal channel, it dampens the rushing sound of water. In my side-by-side test, the Korky was about 30-40% quieter than the standard valve it replaced. For an ensuite bathroom where you don’t want to wake your partner, this is the killer feature.
• Compact “Internal Float” Design: The sleek, column-like shape is a lifesaver for crowded tanks. If you have a modern “low-boy” toilet or a canister flush valve (like in many Kohlers) that takes up a lot of room, Korky fits where others don’t. There is no external float arm to get hung up on the flapper chain, which is a common cause of running toilets.
• Easy Maintenance for Hard Water: If you live in an area with hard water, sediment can clog the valve. The Korky cap is designed to twist off effortlessly so you can rinse the diaphragm. You don’t need tools to service it. I found this much easier than prying off the snap-cap on other models.
• Refill Adjuster Included: The “Platinum” model comes with a small dial on the refill tube. This lets you control how much water goes into the bowl (not the tank) during the refill cycle. This is brilliant for saving water. If your bowl fills up before the tank shuts off, you are just pouring water down the drain. This dial lets you throttle that back.

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Cons Of Korky

• Finicky Height Adjustment: As I mentioned, the twist-lock mechanism requires a bit of force. If you have weak grip strength or arthritis, unlocking the body to telescope it up or down might be difficult. You have to twist the entire head of the valve, and if it’s wet, it can be slippery.
• Slower Fill Time: Because it prioritizes quietness, the water flow is slightly restricted. It took about 10 seconds longer to fill my standard 1.6-gallon tank compared to the Fluidmaster. In a household with five people fighting for the bathroom in the morning, that extra wait time for a double flush might be annoying.
• Refill Tube Clip Issues: The little plastic angle adapter that clips the refill tube to the overflow pipe felt a bit flimsy to me. It didn’t grip the pipe as securely as I would have liked, and I worried it might pop off if the water pressure surged.

Maintenance Tips For Korky

• Clean the Strainer: Korky valves have a small strainer at the very bottom where the water enters. If your fill speed drops dramatically, don’t buy a new valve yet. Remove the valve, pull out the strainer from the bottom shank with needle-nose pliers, and rinse out the grit.
• Replace the Cap, Not the Valve: If the toilet starts running, it’s usually just the rubber diaphragm inside the cap that has worn out. You can buy a “Korky Cap Assembly” (R528) for a few dollars. Replacing just the cap takes 30 seconds and saves you from reinstalling the whole unit.
• Check the Lock: Every few months, just give the body a gentle tug upwards. If it moves, it wasn’t locked properly. Re-twist it to ensure the height setting doesn’t drift over time.

My Experience With Fluidmaster

The Fluidmaster 400A is the Toyota Corolla of plumbing: it is everywhere, it works, and it is cheap.

I installed this in my master bath.

Unlike the Korky, the Fluidmaster has a large grey cup that slides up and down the black shaft. This is the float.

Installation felt incredibly familiar. The height adjustment on the Fluidmaster is, in my opinion, superior to Korky.

You just turn the threaded shank to screw the valve up or down.

It allows for micro-adjustments without unlocking the whole unit. You can dial it in exactly to the water line.

Performance-wise, it is a workhorse. It fills the tank fast.

It has a distinct “hiss” when filling, which lets you know it’s working.

I actually appreciate the sound because if I hear it running when no one is in the bathroom, I know immediately that something is wrong. With the Korky, I might miss a leak because it is so quiet.

Pros Of Fluidmaster

• The Universal Standard: There is a reason this is the best-selling fill valve in the world. It fits almost everything (except very specific low-profile toilets). If you walk into any hardware store—or even a grocery store—you can find a Fluidmaster 400A or a replacement seal for it. You will never be stuck waiting for parts.
• Micro-Adjustable Height: The screw-style height adjustment is brilliant. You can install it, turn the water on, and then twist the shank to raise or lower the water level by a fraction of an inch while the tank is full. This precision helps you get the maximum flush power without wasting water down the overflow tube.
• Fast Refill Speed: The 400A flows freely. It fills the tank rapidly, which is great for high-traffic bathrooms. If you have kids who flush back-to-back, the Fluidmaster recovers much faster than the Korky QuietFill.
• Reliability: I have Fluidmaster valves in rental properties that have been working for 10 years without a hiccup. The design is simple and robust. The external float cup is less prone to getting stuck by mineral deposits compared to older ball-and-arm designs.

Cons Of Fluidmaster

• External Float Vulnerability: The floating cup (the big grey part) slides up and down the main shaft. If you install it too close to the side of the tank, the cup can rub against the porcelain and get stuck, causing the toilet to run. You have to be careful to orient it perfectly so it has clearance on all sides.
• Ideally Louder: It is not “loud” per se, but compared to the Korky, it is definitely audible. In the middle of the night, you will hear the shhhhuuuush of the tank refilling through the bedroom wall if you have thin insulation.
• Cap Replacement is Tricky: To replace the seal (the 242 washer), you have to push down and twist a plastic cap while a spring pushes back against you. It can be a bit of a thumb-wrestle. If you aren’t careful, the cap can fly off or the plastic tabs can snap.
• Visual Bulk: It looks like a piece of industrial machinery inside your tank. While no one really looks inside the tank, the larger footprint makes it harder to work around if you need to replace the flapper later.

Maintenance Tips For Fluidmaster

• The 242 Seal: If your Fluidmaster keeps running, 90% of the time you just need the “242 Replacement Seal.” It costs about $3. Turn off the water, snap the cap off, swap the black rubber washer, and snap it back on. It is one of the cheapest and easiest home repairs you can do.
• Flush the Debris: When you install a new Fluidmaster, the instructions tell you to flush the line without the cap on. Do not skip this. It blows out any rust or pipe scale that might otherwise get stuck in your new seal immediately.
• Check the Refill Tube: Make sure the small black rubber refill tube has an arch to it and isn’t shoved down inside the overflow pipe. If it is inserted too far down, it can create a siphon that sucks water out of the tank, causing the valve to turn on and off phantomly.

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Comparison with other brands

• Kohler Genuine Valves: If you buy a Kohler valve, open the box and look closely. It is often just a rebranded Fluidmaster with a different colored cap. Kohler frequently sources their parts from Fluidmaster. Unless you need a very specific canister valve, you are usually safe (and richer) buying the standard Fluidmaster 400A instead of the “Genuine Kohler” part.
• Brass Ballcocks: You might still have an old-school brass valve with a giant copper float ball. These are antiques. They are durable but incredibly noisy and inefficient. Both Korky and Fluidmaster are massive upgrades over this 1950s technology. Do not try to repair a brass ballcock; just replace it.
• Toto Generic Replacements: If you have a Toto toilet, be careful. While Fluidmaster fits many, Toto toilets often require a specific refill ratio to flush properly. Korky (specifically the 528MP) is often the recommended aftermarket replacement for Toto because its refill ratio is more adjustable than the standard Fluidmaster.

Frequently Asked Questions (FAQ)

Conclusion

The battle between Korky and Fluidmaster ends in a draw, but for different users.

If you want a “set it and forget it” repair that is cheap, reliable, and available at every grocery store in America, buy the Fluidmaster 400A. It is the standard for a reason. The height adjustment is intuitive, it fills fast, and replacement seals are ubiquitous. It is the best choice for the average homeowner who just wants the toilet to stop running.

However, if you are annoyed by noise or have a cramped, modern toilet tank (like a Toto), the Korky QuietFill Platinum is the superior upgrade. Its silent operation is genuinely impressive, and the compact footprint ensures it won’t get tangled up in your flush chain. I now keep Fluidmasters in my rental toolkit for quick fixes, but I use Korky in my own home for the peace and quiet.