Tank Fit

Kohler

Cimarron and Class Five: buy the canister seal, not a flapper

Class Five is Kohler's canister flush system. Lift the lid and you will see a tall plastic cylinder that rises straight up when you flush, instead of a rubber flap hinging open. The wear part is a ring seal on the bottom of that canister, and this is the clearest case on the whole site for buying the OEM part.

How to confirm you have a canister, not a flapper

  • The center of the tank is occupied by a wide plastic cylinder, roughly 3 inches across, connected to the handle by a plastic rod or a short chain to a lift arm.
  • Flushing lifts the whole cylinder vertically. Nothing hinges.
  • The cylinder usually twists off counter-clockwise for service — a quarter turn, then lift.
  • Under it is a black or red rubber ring sitting on a wide seat. That ring is the part.

Why universal flappers go wrong here

Adapter kits exist that convert a canister opening to accept a flapper. They can stop a leak. What they also do is change how fast the tank dumps, and Class Five's flush performance is built around the canister's near-instant full-diameter opening. The predictable outcome is a toilet that no longer clears in one flush, which is worse than the leak you started with. If the canister body itself is intact — and it usually is, it's just the seal that hardens — replace the seal.

Kohler GP1083167Class Five canister flush valve seal (OEM)typically $8–$16
Fits
Kohler Class Five canister systems, including many Cimarron, Wellworth Class Five, Highline Class Five and Devonshire tanks. Kohler publishes this as the service part for the canister seal — check your model's parts diagram on Kohler's site to confirm the number for your exact K- number.
Does not fit
Any 2-inch or 3-inch flapper toilet, TOTO G-Max, and Kohler models that predate Class Five or use AquaPiston with a different seal number. Buying by model name alone is the mistake here — buy by the K- number stamped in your tank.
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Replacing the seal — ten minutes, no tools

  1. Close the supply stop and flush. Sponge the last inch of water out.
  2. Unhook the chain or lift rod from the canister top, then twist the canister counter-clockwise about a quarter turn and lift it out.
  3. Peel the old seal off the bottom of the canister. Note its orientation — these seals are not symmetrical; one face is flat and one is contoured.
  4. Wipe the seat in the tank floor clean. If it feels gritty, soak a paper towel in white vinegar and lay it on the seat for twenty minutes, then wipe again.
  5. Press the new seal on dry, seat the canister, twist to lock, reconnect the chain, open the water.
  6. Dye test after fifteen minutes to confirm.

Two Cimarron symptoms that are not the seal

Weak flush with no leak: check that the water level reaches the mark. Class Five needs its designed head of water; a fill valve set half an inch low reads as a bowl-clearing problem.

Handle feels loose or flushes only when held: the plastic lift arm or the trip lever nut. Note that toilet tank handle nuts are usually reverse-threaded — turn the direction that feels wrong.

Fill valve side

On two-piece Class Five tanks the fill valve is usually a standard bottom-entry part, so a Fluidmaster 400A or Korky QuietFILL fits if your floor-to-overflow measurement clears 9 inches. On one-piece Kohler models (San Souci, Santa Rosa and similar) measure first — several are too short for the universals, which is covered on the does-not-fit page.

Finding your K- number

Kohler stamps the model number inside the tank, usually on the back wall above the waterline, and often molded into the underside of the tank lid. Search that number on Kohler's own site to reach the exploded parts diagram. That diagram, not a marketplace compatibility list, is the authority on which GP part your toilet takes — Kohler has revised service parts across production years while keeping the retail model name unchanged.

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