A leaking flapper is the #1 cause of a running TOTO toilet — same as every other US brand. TOTO's flapper engineering is conservative and reliable; the part typically lasts 5–8 years in normal use before the rubber hardens or mineral deposits build on the seal. Replacement is one of the cheapest plumbing repairs you can do — $6–$15 part, 10 minutes if you have the right size flapper.
Drake II uses a 3-inch flapper — not the standard 2-inch
TOTO's Drake II (their volume Double Cyclone flush model) and most other modern TOTO 1.28 GPF and 1.0 GPF designs use a 3-inch flush valve — wider than the legacy 2-inch found on the original Drake and older models. The wider valve moves water faster for stronger bowl-cleansing at lower GPF. This means:
- Drake II, UltraMax II, Aquia IV, Vespin II need a 3-inch flapper (Korky 2032BP or TOTO THU135S).
- Original Drake (CST744SL), older Eco Drake, older UltraMax need a 2-inch flapper (Korky 100 or Fluidmaster 502P21).
How to verify: Drain the tank. Look down at the flapper. A 2-inch flapper is about the size of a US silver dollar. A 3-inch flapper is the size of a coffee mug rim. Don't guess — measuring saves you the return trip.
Flapper-failure diagnosis (the food-coloring test)
Drop 6–8 drops of food coloring into the tank. Don't flush. Wait 30 minutes. Check the bowl:
- Bowl water is colored = flapper leaks. Replace.
- Bowl water is clear = flapper seals. The running you're hearing is from somewhere else (fill valve, refill tube, supply line, or wax ring failure).
Other flapper-failure symptoms:
- Toilet refills intermittently when nobody's flushed it (the "ghost flush")
- Hissing sound when not in use
- Bowl water level slowly drops between uses
- Tank takes longer than 90 seconds to refill
What to buy
- Korky 2032BP (universal 3" flapper) — $7–$12. Fits Drake II, UltraMax II, Vespin II, Aquia IV. The volume aftermarket pick. UV-resistant rubber, chlorine-tolerant.
- Korky 100 (universal 2" flapper) — $4–$8. Fits original Drake, Eco Drake, older UltraMax. Includes universal chain.
- Fluidmaster 502P21 (2" universal) — $6–$10. Adjustable flapper float for water-saving customization.
- TOTO THU135S (3" OEM flapper for Drake II series) — $14. Genuine TOTO part. Performance comparable to Korky aftermarket.
- TOTO THU272S (2" OEM flapper for original Drake) — $12. Genuine TOTO part.
- Korky 463BP universal adjustable — $10. Fits both 2" and 3" valves. The "I'm not sure which I have" buy.
Replacement procedure (10 minutes)
- Shut off water at the wall.
- Flush to drain the tank. Hold the handle down for a long flush.
- Sponge out remaining ~1/2" of water.
- Unhook the chain from the trip lever arm.
- Lift the old flapper off the overflow tube pegs. Some flappers slide off; some snap off — gentle upward pull.
- Clean the flush valve seat (where the flapper sat). Wipe mineral residue with vinegar-soaked cloth.
- Install the new flapper. Slide onto the overflow tube pegs. Hook the chain to the trip lever with about 1/2" of slack.
- Turn water back on. Tank refills. Test flush.
- Repeat the food-coloring test 24 hours later to confirm the seal holds.
The TOTO-specific flapper issue: longer chain on Drake II
TOTO Drake II tanks are slightly taller than competitors. After installing an aftermarket Korky flapper, the included chain is sometimes too short to reach the trip lever cleanly. Two solutions: (a) extend with a small wire link (any hardware store), or (b) buy the TOTO THU135S OEM flapper which includes a longer-than-standard chain pre-installed.
What if the new flapper still leaks?
- Verify the size — 2" vs 3" mismatch causes immediate leaks.
- Check chain slack — 1/2" is the sweet spot.
- Inspect the flush valve seat for cracks or pitting. Pitted seat = leak no matter the flapper.
- Check for the canister-style flush valve — some Aquia IV revisions use a TOTO-proprietary canister, not a traditional flapper. See our TOTO flush valve page.