TOTO Toilet Flapper Replacement: THU500S or a Seal?

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Quick answer from a licensed plumber: TOTO’s parts manuals list its 3-inch THU500S flapper for the Drake CST743S, Entrada, Ultramax, Ultimate, Ultramax II and Carlyle II, and TOTO says it replaces twelve older flapper numbers. But the 1.28 gpf Drake with Tornado Flush and the Eco Ultramax E-Max list no flapper; their flush valve takes a THU407 seal gasket. Read the model number stamped inside the tank and check its parts manual first.

TOTO with a 3-inch flapper? TOTO’s current part is the THU500S. See the TOTO THU500S on Amazon

TOTO Flappers and Seals at a Glance

These are the parts TOTO lists in its own parts manuals for some of its best-known two-piece and one-piece toilets:

The pattern is the useful part: most of these tanks take the same 3-inch THU500S, but the 1.28 gpf Drake with Tornado Flush and the Eco Ultramax E-Max manuals list no flapper at all. “Tornado Flush” alone does not settle it: the Ultramax II and Carlyle II are also 1.28 gpf Tornado Flush toilets, and their manuals list the THU500S. On the 1.28 gpf Tornado Flush Drake and the E-Max Eco Ultramax, the flush valve is serviced with a seal gasket, THU407, so there is no flapper to replace.

Step 1: Find the Model Number in the Tank

TOTO says the model number is “stamped or engraved in the porcelain” on the china walls inside the tank, as letters plus a three-digit number with possibly more letters after it. Its examples include ST743E, CST 854, C733 and MS974CEFG. TOTO says the most common location is the back wall of the tank or the right-hand wall opposite the trip lever, and the stamp may be on the tank lid too. A code starting with # and two digits (for example #01, Cotton White) is the color, not the model.

With the model number, find your toilet’s parts manual on totousa.com. The replacement flapper, seal and fill valve are listed by part number there, which is where every row in the table above came from.

Step 2: Flapper, Seal or Fill Valve? Do TOTO’s Test

TOTO’s own “no tools needed” test tells you which part is leaking:

1. Let the tank fill, close the shutoff valve, mark the water level and leave it overnight. If the level drops, it is the flapper or the flush valve.
2. Hold the handle down so the water drains to where the flapper and flush valve meet, and leave it overnight. If the level holds there, the flapper is the problem.
3. If the water drops to the bottom of the flush valve, where it meets the china, TOTO says “the gasket at the base of the flush valve is bad.”
4. If the level in step 1 never dropped, it is most likely the fill valve: water going over the top of the overflow tube, or hissing or dripping from the refill tube. Our TOTO fill valve guide lists the fill valve TOTO names for each model.

I send an occasional note when a new guide goes up — repairs worth doing yourself, and the parts that actually last. No spam, no course funnel; written by a licensed Georgia plumber.

Step 3: Swap the Flapper the Way TOTO Describes

1. Shut the water off at the angle stop, lift the lid off carefully, and flush while holding the handle down to drain the tank.
2. Unhook the chain from the trip lever arm and note which hole it was in.
3. Slide the flapper arms off the plastic pegs on the flush valve, and slide the new flapper’s arms on.
4. Hook the chain to the same hole, with a little slack when the flapper is closed.
5. Turn the water on, let the tank fill and test the flush.

The THU500S listing says it comes with a chain and set-up instructions specific to each TOTO tank model, so follow that sheet for your tank. And if you ever replace the handle, note TOTO’s warning that the trip lever locknut is reverse threaded.

Dual Flush TOTO Toilets

On a dual flush TOTO, TOTO’s repair for a leak is at the flush tower, not a flapper. TOTO’s steps, for a dual flush toilet that is not wall hung: close the supply, note which way the tower’s refill port faces, remove the refill tube, twist the upper part of the tower counterclockwise and lift it out, turn it over and replace the rubber seal gasket, then reinstall it, turn it clockwise until the refill port faces the front again, and reattach the refill tube. Buy the gasket your model’s parts manual lists. Shopping for a dual flush toilet? See single flush vs dual flush toilet.

What to Buy

Genuine TOTO parts, matched to the table above:

• THU500S flapper: TOTO THU500S 3-inch replacement flapper, sold by Amazon, or the TOTO THU500S 2-pack if you have two toilets. Both listings are TOTO-branded and print the same list of replaced part numbers as TOTO’s store.
• THU407 seal gasket (1.28 gpf Tornado Flush Drake, Eco Ultramax E-Max): we did not link one. When we checked, the only THU407 listings on Amazon were third-party “compatible” packs, not TOTO parts. TOTO says its replacement parts are available at the TOTO Parts Store.

Parts You’ll Also Need

Usually the flapper is the whole repair. If the fill valve is the leak:

• A fill valve, only if TOTO’s test points to it: TOTO adjustable replacement fill valve assembly, sold by Amazon. Its listing says it is adjustable for all TOTO tanks and has a standard 7/8-inch inlet, but it prints no TOTO part number, so compare it with the fill valve your parts manual lists (TSU708, TSU81.30-A, TSU51A or TUS99A.X in the table above). TOTO’s instructions for its universal fill valve say to set the height and refill key from the fit chart for your model before you install it.

When to Call a Licensed Plumber

• TOTO’s test says the flush valve gasket is bad; on a two-piece toilet that means lifting the tank off the bowl.
• You have a TOTO with a WASHLET or an auto-flush unit and water is getting near the electrical parts.
• The angle stop will not shut off, so you cannot drain the tank.

FAQ

What flapper does a TOTO Drake use?

It depends on the Drake. TOTO’s parts manual for the Drake CST743S (G-Max) lists the THU500S flapper. Its manual for the 1.28 gpf Drake with Tornado Flush (C776CE and related) lists no flapper; that flush valve uses a THU407 seal gasket.

Is the TOTO THU500S universal?

For TOTO’s 3-inch flush valves, largely. TOTO’s parts store says the THU500S replaces THU138S, THU175S, THU331S, THU140S, THU299S, THU253S, THU277S, THU347S, THU275S, THU332S, THU369S and THU499S. TOTO also sells 2-inch flappers, so confirm your size first.

Where is the model number on a TOTO toilet?

Stamped or engraved in the porcelain inside the tank, usually on the back wall or on the right-hand wall opposite the trip lever, per TOTO. It may also be on the tank lid. It looks like ST743E or CST854.

Why is my TOTO still running after a new flapper?

Do TOTO’s overnight test. If the water drops to the bottom of the flush valve, the gasket at its base is bad. If the level never drops, TOTO says the fill valve is most likely the problem. Also check the chain has a little slack.

How do I fix a leaking dual flush TOTO?

TOTO’s repair is at the flush tower: twist the upper part of the tower counterclockwise and lift it out, turn it over, replace the rubber seal gasket, and turn it back in until the refill port faces the front. TOTO gives these steps for dual flush toilets that are not wall hung.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. Every part number, size and fit on this page comes from the manufacturer pages and documents listed below, which we opened and read; product details come from those makers and from the Amazon listings, not from hands-on testing. Each linked product was shipped or sold by Amazon, new and in stock, when we checked on September 24, 2026. Nobody pays to be included here. Where a link goes to Amazon we may earn a commission at no extra cost to you. More on who writes this and how we pick.

Sources

• TOTO USA: Product FAQ (replacement parts, flapper, fill valve, flush tower, model number)
• TOTO Parts Store: 3″ Universal Toilet Flapper THU500S and 2″ flappers
• TOTO parts manual PD-00237: Drake CST743S
• TOTO parts manual PD-00758: Entrada CST243EF
• TOTO parts manual PD-00346: Ultramax MS854114S/SG
• TOTO parts manual PD-00345: Ultimate MS854114
• TOTO parts manual PD-00640: Ultramax II MS604114CEF(G)
• TOTO parts manual PD-00539: Carlyle II MS614114CEF(G)
• TOTO parts manual PD-01375: Drake 1.28 gpf Tornado Flush (C776CE and related)
• TOTO parts manual PD-00160: Eco Ultramax 1.28 gpf E-Max

Bottom Line

Read the model number off the china, open its TOTO parts manual, and buy what it lists: usually the THU500S flapper, but a THU407 seal on a 1.28 gpf Tornado Flush Drake or an E-Max Eco Ultramax. Run TOTO’s overnight test first so you replace the part that is actually leaking.