Guides · Bathroom

How to replace a toilet flapper

The rubber seal at the tank bottom that lifts on flush. A worn flapper runs silently 24/7 and is the #1 cause of phantom toilet water bills.

Replacement cost

$3–$12

Typical lifespan

3 yrs

Maintenance

every 6 months

Difficulty

Easy

Why the flapper is the usual suspect

The flapper is the rubber seal at the bottom of the tank. Every flush lifts it open and every refill drops it back down, so it lives a hard life — chlorine and mineral-heavy water slowly stiffen the rubber until it no longer seats flat. A worn flapper lets water trickle into the bowl around the clock, which shows up as a tank that refills on its own, a faint running sound, or a water bill that creeps up for no visible reason.

Confirm the leak in five minutes

Before buying anything, run the food-coloring test: drip a few drops of food coloring into the tank and wait without flushing. If color appears in the bowl, the flapper is leaking past its seat. The catalog suggests checking this about twice a year — it is the cheapest diagnostic in home plumbing.

What you need

None (or scissors to trim chain)

One thing to check before shopping: look at the drain opening at the tank bottom. Flappers come in 2-inch and 3-inch sizes, and brands differ in how the flapper attaches (ears on the overflow tube versus a ring that slides over it). Take the old flapper with you, or note the brand and toilet model on the inside tank wall.

The steps

Turn off the supply valve and flush to empty the tank.
Unhook the flapper from the flush valve ears and slip it off the overflow tube.
Hook the new flapper onto the ears and tube; adjust chain slack (1-2 links).
Restore water, flush twice, and confirm the tank seals without trickle.

If it still runs

A running tank right after the swap is usually chain slack, not a bad part: too tight and the flapper never seats; too loose and it catches under the flap. Adjust a link or two at a time. Water level is the second check — the fill valve should stop about an inch below the top of the overflow tube, and the small tube from the fill valve should drip into that tube, not over it.

If a new, correctly adjusted flapper does not stop the leak, the leak may be at the flush valve seat itself or the fill valve — those are bigger jobs inside the tank, and at that point it is reasonable to have a plumber take a look.