Short definition
A flapper is the hinged rubber seal at the bottom of a toilet tank that sits on the flush-valve seat. Pressing the flush handle raises the flapper via a chain; water rushes from tank to bowl; as the tank empties, the flapper sinks back onto the seat and refill begins. It’s the most-replaced toilet part in residential plumbing — and the cause of nearly every running-toilet complaint.
What it is
A flapper is a hollow rubber dome with a hinge ring at one side and a chain attachment loop at the top. The hinge slips over two pegs at the base of the overflow tube; the chain connects to the flush lever. At rest, the flapper’s weight (plus the water column above it once water drops) holds it tight against the flush-valve seat — sealing the tank.
Standard flapper sizes match the flush-valve seat: 2 inch (most pre-2005 toilets), 3 inch (most modern 1.28 gpf high-efficiency toilets), and 4 inch (large-trapway designs). Match the size before buying.
Brands that ship current 2026 product include Korky, Fluidmaster, Kohler-OEM, and Toto-OEM. WA-relevant: standard rubber flappers in chloraminated water (most major WA utilities) typically last 2 to 5 years before they soften and stop sealing. Chloramine-resistant (“hard-water flapper”) versions extend that to 5 to 10 years.
Why it matters to a homeowner
Flapper failure is the single highest-frequency toilet repair. Symptoms: continuous running, phantom flush (toilet briefly refills on its own every few hours), or a slow trickle visible from tank to bowl. The standard diagnostic is a dye test — drop food coloring (or a free Saving Water Partnership dye tablet) in the tank, wait 15 to 30 minutes without flushing, and check the bowl. If the bowl water tints, the flapper leaks.
The repair is honest five-minute DIY: shut off the angle stop, flush to drain the tank, unhook the chain, slip off the flapper from its hinge pegs, slip on a new one, reattach the chain (with a touch of slack — too tight prevents full closure, too loose limits flush volume).
A constantly leaking flapper can waste 200-plus gallons per day in severe cases, 20 to 50 gallons per day in typical ones. Annual water-bill savings from a flapper fix range $50 to $300 depending on local rates.
Common failure modes
- Worn / softened rubber. Flapper won’t seat fully; constant trickle. Top WA-water cause.
- Warped flapper. Heat or chemical exposure deforms it. Same symptom.
- Chain too tight. Flapper can’t fully close.
- Chain too loose. Flapper not lifted high enough on flush; weak flush.
- Flapper hooked on the overflow tube. Won’t drop after flush; tank drains completely.
Common variants
- Standard flapper vs. canister flush valve. Modern Toto and Kohler toilets often use canister-style valves instead of flappers — different repair.
- Standard rubber vs. hard-water (chloramine-resistant) flapper. Premium for WA water service; lasts 2 to 3 times longer.
- 2 inch vs. 3 inch vs. 4 inch. Sized to flush-valve seat; verify before buying.