How to Identify Your Toilet Flush Valve [2026]

Pull off the tank lid to fix a running toilet and you’ll find one of two very different things: a rubber flapper hinged over a hole, or a tall plastic canister with no flapper in sight at all. How to identify your toilet flush valve starts with figuring out which of those you’re actually looking at, because the flapper aisle at the hardware store won’t help you if your toilet uses a Kohler canister, a Mansfield tower, or an American Standard Champion valve with a 4-inch opening.

The fix is usually cheap – a universal flapper runs $4 to $10 – but only if it’s the right size and the right style. This guide walks through where to find your toilet’s model number, how to read the flush valve itself for visual clues, and what to do when both come up blank.

How to Identify Your Toilet Flush Valve: Start With the Tank, Not the Valve

The flush valve is usually selected by the toilet’s tank model and flush-volume rating, not by what the loose rubber or plastic part looks like sitting in your hand, so the fastest path to the right part is identifying the toilet itself first Korky. Lift the tank lid, set it aside carefully, and shine a flashlight across the inside back wall of the tank – that’s where most manufacturers stamp, mold, or barcode the model number, cast date, and water-use rating Gerber.

Kohler tank numbers commonly use a K- prefix, such as K-4418 or K-4708-AA, embossed into the porcelain – easy to mistake for a generic casting mark if you don’t know to look for it Kohler support. TOTO’s own numbering system uses a letter prefix to separate part types: bowl model numbers start with C, ceramic tank numbers start with S, resin tank numbers may start with TCF or CES, and any number starting with # is a color code, not the model TOTO. A Home Depot customer photo of an American Standard Champion tank shows the model 4149A, a 1.6 gpf / 6.0 Lpf rating, and a stamped date, all inside the tank – exactly what you should photograph before shopping for a flush valve Home Depot.

If the back wall is blank or hidden behind hardware, check the right and left interior side walls next – TOTO in particular sometimes places its model number on the wall opposite the trip lever PlumbingSupply. Mineral staining or foam tank insulation can also obscure a marking near the waterline, so a damp cloth and a flashlight held at an angle often reveal a number that looks blank at first glance PlumbingSupply blog.

Check the Tank Lid, the Exterior, and Any Loose Parts

If the tank interior is a dead end, flip the tank lid over. Some manufacturers use a paper or adhesive label on the underside rather than an embossed number, and Korky’s identification diagram points homeowners to exactly three spots in this order: the lid underside, the tank interior, and the exterior brand name Korky. One caution: a replacement lid bought separately or from a salvage seller can carry a different model number than the tank body, so trust the tank’s own markings over a lid that might not be original PlumbingSupply.

The exterior brand logo narrows the search but rarely finishes it, since a single brand often sells several incompatible flush-valve families Korky. TOTO notes its bowl mark and product-number label may sit on the lower side of the bowl, and Gerber says its two-piece bowl model numbers can be found under the bowl rim, readable with a mirror or phone camera without removing the toilet TOTO Gerber.

Don’t confuse a flapper’s own size with the toilet’s tank model number – a 2-inch or 3-inch universal flapper fits many brands but doesn’t tell you which brand you own, and it won’t fit a proprietary canister, tower, or Champion-style valve at all Korky. If the tank contains a sealed black pressure vessel instead of an open flapper or canister, you’re looking at a pressure-assist system, and Gerber notes those model numbers are still found inside the tank – it still needs to be opened and photographed before you order parts Gerber.

Visual ID by Flush Valve Type

Once you’ve got a model number (or even without one), the physical shape of the valve tells you a lot on its own.

Standard 2-inch flapper. A hinged rubber or plastic flapper sits over an overflow tube with a chain running to the trip lever. Korky says most toilets built before 2000 use this standard 2-inch size, and the drain opening is roughly orange- or baseball-sized Korky. A 2-inch universal flapper from Korky is sold to fit many Kohler, Glacier Bay, and American Standard models built to this spec Lowe’s.

Large 3-inch flapper. Visually wider – grapefruit- or softball-sized rather than baseball-sized – and common on many toilets built since 2005 to meet 1.6 gpf and 1.28 gpf water-use standards Korky. Korky’s 3-inch universal flapper lists compatibility across Kohler, TOTO, American Standard, Gerber, and Mansfield model families built to this larger opening Lowe’s.

Kohler canister (AquaPiston-style). No flapper at all – instead, a tall canister lifts vertically off a circular seal at the base of the tank SupplyHouse. A leaking Kohler canister toilet usually needs a replacement seal like the yellow GP1059291, sold specifically for single-flush canister toilets as a replacement for the earlier red seal – not a flapper of any size Lowe’s.

Mansfield tower. A vertical tower mechanism instead of a hinged flapper. Korky’s Mansfield-specific kit is built to fit the 208, 209, 210, and 211 tower-style valves and adjusts to cover both 1.6 gpf and 3.5 gpf versions Korky. Home Depot also carries a dedicated 1.6 gpf replacement valve for the Mansfield 211, which is one of the more commonly searched Mansfield part numbers Home Depot.

American Standard Champion. The Champion 4 line uses a very large flush-valve opening – Home Depot’s listing for the Champion 4 Max tank states it ships with a full 4-inch flush valve, which means a standard 3-inch universal flapper is the wrong assumption for this family Home Depot.

TOTO with an Eco suffix. TOTO’s identification is mostly model-number driven, but a letter E appended to a familiar tank number – such as ST743E versus the original ST743 – flags an Eco version with a different flush volume (1.28 gpf instead of 1.6 gpf), which can mean a different flapper or flush valve is needed even though the base model number matches PlumbingSupply.

Dual-flush retrofit. A push-button handle instead of a side lever usually signals a retrofit kit rather than an original part. Danco’s HydroRight kit, for example, is an aftermarket cylindrical valve body with a push-button handle that converts a standard toilet to dual-flush – treat it as an add-on unless the tank’s own label confirms the toilet shipped that way originally Home Depot.

Valve family	Fastest visible clue	Size or feature cue	Parts warning
Standard flapper	Hinged rubber flapper on an overflow tube	About baseball-sized opening (2 in.) Korky	Common on toilets built before 2000
Large flapper	Hinged flapper, visibly wider	About softball-sized opening (3 in.) Korky	Common on many 1.6/1.28 gpf toilets since 2005
Kohler canister	Tall vertical canister, no flapper	Circular seal at the base SupplyHouse	Needs a canister seal (e.g. GP1059291), not a flapper Lowe’s
Mansfield tower	Vertical tower mechanism	Fits Mansfield 208/209/210/211 families Korky	Needs a tower-style kit, not a hinged flapper
American Standard Champion	Very large valve opening	4-inch flush valve on Champion 4 Home Depot	A 3-inch universal flapper will not seal it
TOTO Eco (E suffix)	Same base tank number plus E	1.28 gpf vs. 1.6 gpf original PlumbingSupply	Confirm the suffix before ordering a flapper

Manufacturer and Retailer Lookup Tools

Korky’s Toilet Genius tool is built for exactly this problem – it asks whether your valve is a flapper, tower, Kohler-style, Mansfield-style, Champion 4, Champion 3, or dual-flush design, then narrows to a compatible part Korky. It’s strong for aftermarket flappers and visual matching, but it can’t replace a manufacturer’s service-parts diagram for a proprietary OEM-only valve Korky.

PlumbingSupply’s TOTO picture-reference tool is useful once you have a tank number like ST743E, since it links straight to a parts schematic PlumbingSupply. Gerber’s support page is the strongest single reference for where model numbers, cast dates, barcodes, and serial codes appear across bowls, tanks, and pressure-assist tanks Gerber, and Kohler’s own identification article covers tank numbers, access-panel labels, and shell markings Kohler support.

Home Depot and Lowe’s product pages are a useful cross-check, since customer Q&A photos often show the exact tank markings you’re trying to match Home Depot. They’re weakest wherever “universal” is the pitch – a universal flapper covers many 2-inch or 3-inch openings, but never a proprietary tower, canister, or Champion valve Lowe’s. Once you’ve matched a valve family from the table above, our free Repair Finder can help confirm the exact part before you make a trip to the store.

What to Do If You Still Can’t Identify the Valve

Start with photos, not measurements alone: the tank interior, the flush valve from above, the trip lever, the lid underside, and any stamped numbers on the bowl or tank Korky. For a standard flapper design, measure the drain opening – or compare the old flapper – before buying anything Korky. A 2-inch flapper is the right generic guess for older gravity toilets, a 3-inch flapper for newer high-efficiency models; if unsure, a dual-size flapper like Fluidmaster’s Super Flapper (configurable for either size) reduces the risk of a wrong-size return trip Lowe’s.

A tower, canister, Champion, pressure-assist, or dual-flush design needs its own family of parts – generic flapper logic won’t get you there Korky. A Kohler canister with a bad seal needs a canister seal, not a flapper Lowe’s; a Mansfield tower needs a Mansfield-compatible tower kit Korky; a Champion tank with a 4-inch opening needs Champion-compatible parts Home Depot.

Replace the whole flush valve – or the toilet – when the porcelain around the valve opening is cracked, the tank-to-bowl seal is leaking from damaged porcelain, a pressure-assist vessel is obsolete, or chasing proprietary internals starts to cost as much as a new toilet The Spruce. Treat that as a last resort for missing IDs or discontinued parts – not the first answer for an ordinary worn flapper Gerber.

When to Call a Plumber for ID

Some identification problems aren’t worth solving yourself. Call a plumber when reaching the markings requires removing the tank, the tank bolts are corroded, the shutoff valve won’t close, the toilet is pressure-assist, there’s an active tank-to-bowl leak, or a one-piece/skirted toilet hides its markings behind an access panel or shell Gerber. Kohler’s own support images show some model information sits behind an access panel or under the shell on certain designs – a reasonable stopping point if disassembly risks cracking anything Kohler support.

A short plumber visit can also be the cheaper option when the symptom could be the flapper, the valve body, the tank-to-bowl gasket, or the fill valve, and you genuinely can’t narrow it down Korky. Plumber rates commonly run $75 to $150 per hour, and a 30-minute identification call often costs less than two or three wrong parts orders on a proprietary valve The Spruce – a much smaller job than full toilet installation, so don’t let ID trouble alone push you toward replacing the whole fixture.

What to Do Next

Once you know whether you’re dealing with a flapper, a canister, a tower, or a Champion-style valve, our guide to replacing a toilet flush valve walks through the swap step by step. If you’ve confirmed you need a flapper but aren’t sure which size, What Size Flapper Do I Need? covers the 2-inch versus 3-inch measurement in more depth. For identifying the toilet itself – brand, model, and bowl/tank numbers beyond just the flush valve – see How to Identify Your Toilet. And if the toilet is running and you haven’t confirmed the flush valve is the cause, start with Why Is My Toilet Running? 6 Common Causes to rule out the fill valve 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.

Sources

• Korky: Toilet Genius Visual Parts Assistant
• Korky: What Size Flapper Do I Need?
• Korky: Mansfield 210/211 Flush Valve and Seal Kit
• Korky: 2x Long-Life Universal Complete Kit (identification diagram)
• Kohler: Identifying Your Toilet Model
• SupplyHouse: Kohler Canister Flush Valve Assembly Kit for Cimarron Toilets
• Lowe’s: Kohler Yellow Canister Flush Valve Seal (GP1059291)
• TOTO: Product Number Support
• PlumbingSupply: TOTO Toilet Parts Finder
• Gerber Support: Where to Find Your Model Number
• Home Depot: American Standard Champion 4 Max Tank
• Home Depot: Mansfield 211 Replacement Flush Valve
• Home Depot: Danco HydroRight Dual-Flush Retrofit Kit
• Lowe’s: Fluidmaster Super Flapper (2-Inch/3-Inch)
• The Spruce: Toilet Installation Cost Guide

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.

Get the homeowner’s plumbing repair toolkit checklist – the tools, parts, and decisions every homeowner should have on hand. [Free download – enter your email]