Toilet Repair Guide ·11 min read

How to Identify Your Toilet Fill Valve [2026]

By Thomas Kwayne · July 30, 2026 · Fact-checked against manufacturer documentation and authoritative trade sources.

Most homeowners never look at their toilet’s fill valve until it starts hissing, running long after a flush, or refusing to shut off – and by then they’re standing in a hardware store aisle full of look-alike parts with no idea which one is already in the tank. How to identify your toilet fill valve comes down to reading a handful of physical clues in order: the top cap, the side of the float body, the height-adjustment shank, and, if none of that is legible, the model number stamped inside the tank itself.

This guide walks through those clues for the fill valves most common in US homes – Fluidmaster, Korky, Kohler, TOTO, Danco, and American Standard – so you can confirm what’s in your tank before you buy a replacement.

Start With the Top Cap

Lift the tank lid and look at the fill valve’s top cap first. It’s usually the most legible spot because it sits above the waterline and never sees standing water, so mineral scale builds up slower than on submerged parts. Fluidmaster 400A manual

A Fluidmaster 400UK-family cap has “Fluidmaster” and the model number molded directly into the black plastic. A TOTO TSU99A.X replacement valve uses a bright blue cap embossed with “TOTO” and “ANTI SIPHON 529,” making the blue cap itself a fast identifier for TOTO-branded universal valves. Home Depot: TOTO TSU99A.X Kohler’s OEM valves run red or white caps – Home Depot lists the white-cap Kohler Silent Fill kit as model GP1138930. Home Depot: Kohler GP1138930

If the cap is blank or the molding has worn smooth, move down to the body.

Check the Float Chamber and the Refill Tube

Next, look at the side of the float chamber or control box – the wider section below the cap that houses the float mechanism. Korky’s 528MP QuietFILL Platinum shows molded Lavelle Industries markings on this side box, and retailers list it as model 528MP even though an installed valve may only show a silver top, black body, red shank gasket, and that side float chamber once it’s in the tank. True Value: Korky 528MP TOTO’s TSU99A.X pairs a black side box with its blue top, so it’s worth photographing the side even when the cap logo is already visible. The Part Works

The refill tube – the small tube that sends water into the overflow pipe after a flush – is also a clue. A Danco HydroClean valve adds a tank-cleaning jet tube and a small green mini-valve on its side, which sets it apart at a glance from the simpler Fluidmaster and Korky designs. Lowe’s: Danco HC660 And regardless of brand, the refill tube’s end should sit above the water line, not pushed down inside the overflow tube – Fluidmaster warns that a submerged refill tube can siphon the tank and make the valve cycle on and off. PlumbingSupply.com

Brand-by-Brand Visual Cues

When the cap and side markings are both worn off, the body style, adjustment range, and any extra features narrow it down. This table is the at-a-glance version:

Brand / family	Fastest visible clue	Height-adjustment range	Common model
Fluidmaster 400A	Gray/black body, black cylindrical float cup, top water-level adjustment screw, EZ-Twist lower shank	9-14 in.	400A
Fluidmaster PerforMAX	Blue cap over a gray body with the same black float cup	9-14 in.	400H / 400AH
Korky QuietFILL Platinum	Silver top, black body, red shank gasket, side float box	7-3/4 to 13-1/2 in.	528MP
Korky “Fits TOTO”	Blue top, black body, marketed specifically for TOTO refill volume	7-3/4 to 13-1/2 in.	528T
Kohler Silent Fill	White or red cap, black float cup, OEM Kohler packaging	Adjustable	GP1138930 / GP1083167
TOTO universal	Blue cap embossed “TOTO,” black body, red gasket	Adjustable	TSU99A.X
Danco HydroClean	Blue/gray body, green mini-valve, tank-cleaning jet tube, built-in leak detection	11-13.8 in.	HC660
American Standard universal	Black body with a blue cap, styled as a 400A-type repair part	Adjustable	7381125-400.0070A

Two things complicate a brand-by-look match. First, a Kohler or TOTO toilet frequently contains an aftermarket replacement rather than the original OEM valve – a TOTO tank can just as easily hold a Korky “Fits TOTO” 528T as a genuine TOTO part, so tank brand and installed fill-valve brand don’t always match. SupplyHouse: Korky 528T Second, American Standard’s own official repair part is explicitly labeled “Fill Valve Universal 400A,” so an American Standard-branded box can contain a valve that looks nearly identical to a Fluidmaster 400A. American Standard

Older toilets may not use this style of valve at all. A ballcock has a side float ball riding on a lever arm, while every valve in the table above uses a compact float that rides around or beside a central tower – the side-float ballcock is physically wider and visually distinct from the newer concentric-float designs. Wikipedia: Flush toilet

Once you’ve matched a family from the table, our free Repair Finder can help confirm the exact replacement part before you head to the store.

No Marking on the Valve? Read the Tank Instead

If the fill valve itself has no readable marking, shift to the toilet tank’s own model stamp. The inside back wall of the tank commonly carries the toilet’s model number, water-use rating, and a manufacturing date, and that information can point you to the correct OEM fill valve even when the valve itself is blank. Kohler/Mira service portal

American Standard tank walls typically show a model number like “4149A,” a water-use rating such as “6.0 Lpf / 1.6 gpf,” and a molded manufacturing date. Home Depot Q&A photo TOTO tanks carry model strings such as CST854S#01 alongside the water-use rating. Gerber’s support page confirms that most of the information a homeowner needs – model number, manufacturing line code, and a cast date – is stamped on the tank’s back wall, not on the fill valve. Gerber Canada support

For toilet-brand identification generally – not just the fill valve – our guide on how to identify your toilet covers every marking location in more depth, including the bowl and tank-lid numbers.

The practical order to work through: photograph the fill valve’s cap, side body, and refill tube; photograph the tank’s back-wall stamp; search the exact fill-valve model first; and only fall back to the toilet’s tank model if the valve itself is unmarked or clearly an aftermarket replacement. Fluidmaster 400A manual

How to Identify Your Toilet Fill Valve: Quick Decision Tree

Cap has a legible brand and model: search that model number directly – this is the highest-confidence identification.
Cap is blank but the side box or refill tube has a distinct shape: compare against the brand-by-brand table above.
Valve is blank all over: photograph the tank’s inside back wall for its model number and date stamp, and search that instead.
Tank is also unmarked, or the model search doesn’t turn up a match: treat it as a universal-fit situation (next section) rather than guessing at a specific brand.
Toilet is a pressure-assist, wall-hung, or otherwise non-standard tank: stop guessing and call a plumber – these don’t use the gravity-tank fill valves covered here.

What to Do If You Still Can’t Identify It

A blank valve and a blank tank aren’t a dead end. Universal replacements are a legitimate fallback whenever the toilet is a standard gravity-tank design. Fluidmaster’s 400A is sold as a universal fit for most toilet models, Korky’s 528MP is marketed to fit Kohler, TOTO, American Standard, and other 1.6-gpf-and-under tanks, and TOTO’s own TSU99A.X is sold as fitting most toilets on the market. Lowe’s: Fluidmaster 400A True Value: Korky 528MP Home Depot: TOTO TSU99A.X

If the old valve is noisy, slow-filling, leaking, or won’t shut off, replace the whole valve rather than chasing individual internal parts – a complete universal fill valve already includes the shank washer, locknut, refill tube, and clip, and typically costs about as much as a single internal repair kit. Lowe’s: Fluidmaster 400A While the tank is open, it’s also worth replacing the supply connector if it’s worn or of unknown age – Fluidmaster’s own installation instructions specifically call out an old or unknown-age connector as a flooding risk. Fluidmaster 400A manual

When to Call a Plumber for ID

Identification stops being a DIY job once removing the valve becomes risky rather than routine. Call a plumber when the shutoff valve behind the toilet won’t fully close, when the supply connector is corroded or of unknown age, when the tank hardware feels brittle, or when there’s a real risk of cracking the tank trying to pull the old valve out. Fluidmaster 400A manual An overflowing toilet is also a plumber call, not a static identification project. The Spruce

The same goes for pressure-assisted, wall-hung, concealed, or otherwise unusual one-piece tanks – the identification steps in this guide assume a standard gravity tank with a visible float-style fill valve, and a non-standard system needs a different playbook entirely. Wikipedia: Flush toilet

A short identification visit is often cheaper than it sounds next to a wrong parts order. Plumber labor commonly runs $75 to $150 per hour for toilet repair calls, and a 30-minute ID visit can save two trips to the hardware store when the model number is buried under mineral scale or the installed valve is an unmarked aftermarket part. The Spruce

What to Do Next

Once you’ve confirmed the brand and model, our guide to replacing a toilet fill valve covers the swap step by step, including the height setting that trips up most first-time DIYers. If the toilet is running and you haven’t confirmed the fill valve is actually the cause, start with Why Is My Toilet Running? 6 Common Causes to rule out the flapper first. For the rest of the tank and bowl, the Toilet Repair Guide is the Pillar 2 hub and index for every article in this cluster.

Where is the fill valve inside my toilet tank?

It’s the upright valve mounted off-center, directly above where the water supply line enters the bottom of the tank. Don’t confuse it with the overflow tube next to it – the overflow tube is an open pipe tied to the flapper, while the fill valve has a float, an adjustment screw or dial, and a refill tube.

What’s the fastest way to identify my fill valve’s brand?

Check the top cap first – it sits above the waterline and stays legible longer than parts that see standing water. If the cap is blank, check the side of the float chamber and the refill tube style before falling back to the toilet tank’s own model stamp.

My fill valve has no visible markings at all – what now?

Photograph the tank’s inside back wall for its model number, water-use rating, and manufacturing date. Search that toilet model instead of the valve, since the correct OEM fill valve is often tied to the tank model rather than a readable part number.

Does the toilet tank’s brand tell me the fill valve’s brand?

Not reliably. A previous owner or plumber may have installed a universal replacement, so a Kohler or TOTO tank can easily contain a Fluidmaster or Korky valve rather than the original OEM part.

Are toilet fill valves interchangeable between brands?

For standard gravity-tank toilets, yes – universal valves from Fluidmaster, Korky, and TOTO are explicitly sold as fitting most toilet brands. Pressure-assisted, wall-hung, and other non-standard tanks are the exception and need a plumber’s input.

When should I stop trying to identify the valve myself and call a plumber?

Call a plumber if the shutoff valve won’t close, the supply connector looks corroded or too old to trust, the tank hardware feels brittle, or you’re worried about cracking the tank while removing the old valve. A short ID visit, often $75-$150 in labor, is usually cheaper than a wrong parts order.

Sources

Educational content only. Not a substitute for licensed professional advice. Local plumbing codes vary by jurisdiction. Use of any guidance from this guide is at your own risk.

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Fluidmaster 400A Universal Toilet Fill Valve — Height-adjustable 9-14 in. universal fill valve — the safe default when your original valve's brand can't be confirmed.
Korky 528MP QuietFILL Platinum Fill Valve — Adjusts 7-3/4 to 13-1/2 in. and is marketed to fit Kohler, TOTO, American Standard, and other 1.6-gpf-and-under tanks.

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