What is the rubber stopper in a toilet tank called?

The rubber stopper in a toilet tank is called the flapper.

Common names you may hear:

• Toilet flapper (most common)

• Flapper valve

• Flush flapper

• Tank flapper

What it does

The flapper sits at the bottom of the tank over the flush valve opening. When you press the handle, the flapper lifts, allowing water to flow into the bowl. It then drops back down to seal the opening so the tank can refill.

Typical sizes

• 2-inch flapper → standard toilets (most common)

• 3-inch flapper → newer or high-efficiency toilets (Kohler, American Standard, etc.)

Related parts (often confused with the flapper)

• Flush valve – the plastic assembly the flapper seals against

• Tank-to-bowl gasket (spud washer) – large rubber ring between tank and bowl

• Fill valve – controls refilling the tank

💡 Tip: If your toilet runs constantly, a worn or warped flapper is usually the cause.

If you want, tell me your toilet brand or the opening size, and I can tell you exactly which flapper you need.