September 9, 2026 Easy Plumbing

Identifying Your Toilet's Flapper, Flush Valve and Trip Lever

A running toilet is usually a five-dollar part. The hard bit is working out which part. Here is how to identify what you have before you order.

Find the model number first

Almost every toilet carries its model number somewhere you can read without tools:

Inside the tank, on the back wall above the water line. This is the usual spot — a stamped or printed number, often four digits.
Under the tank lid, moulded into the underside.
Behind the seat hinges or on the side of the bowl near the floor.

Note the number and the date stamp if there is one. Manufacturers revise internal components over a model's life, so a 2005 and a 2022 example of the same model can take different parts.

The flapper

The flapper seals the flush valve opening. If your toilet runs intermittently or you hear it refill without anyone flushing, the flapper is the first suspect.

Measure the flush valve opening, not the flapper itself. A 2" opening takes a 2" flapper; a 3" opening takes a 3" flapper. Hold a tape across the drain hole at the bottom of the tank. Getting this wrong is the most common flapper mistake.
Check the mounting style. Some clip onto ears on the overflow tube, others slide over the tube, and some are a solid one-piece canister seal rather than a hinged flap.
Canister flush valves are different. KOHLER's AquaPiston and similar designs use a ring-shaped seal that lifts straight up. There is no flapper to replace — you replace the seal.
Test it by putting a few drops of food colouring in the tank and waiting twenty minutes without flushing. Colour in the bowl means the flapper or seal is leaking.

The flush valve

The whole assembly the flapper seats against. Replace it when the seat itself is pitted, scaled or cracked and a new flapper still will not seal. Replacing a flush valve means removing the tank from the bowl, so it is a bigger job than a flapper — worth doing properly with a new tank-to-bowl gasket and bolts at the same time.

The trip lever

The handle and the arm inside the tank. More variable than people expect:

Mounting position — front, side or angled. A front-mount lever will not fit a side-mount hole.
Hole shape — many tanks have a plain round hole, but some use an oval or D-shaped hole that keeps the lever from rotating. An oval hole needs a lever made for it.
Arm length and bend — has to reach the chain or the canister lift without binding.
Thread direction — the retaining nut inside the tank is often reverse-threaded. Turn it clockwise to loosen.
Finish — levers come in the same finishes as your trim, so match it if it is visible.

The fill valve

If the tank refills slowly, will not shut off, or the water level is wrong, the fill valve is the culprit rather than the flapper. Most modern fill valves are height-adjustable and largely universal, which makes this the easiest of these repairs.

When in doubt, send a photo

A photo of the open tank plus the model number from inside it is normally all we need to identify the exact part. That is far quicker than working through a parts diagram, and it avoids ordering a part that was never going to fit.

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