A running toilet isn’t just annoying — it can waste up to 200 gallons of water per day. That’s real money on your water bill. In 95% of cases, the fix is a $5–$10 flapper that takes five minutes to replace. I’ve replaced thousands of flappers as a plumber. Here are the ones that actually seal properly and last.
| Product | Best For | Price |
|---|---|---|
| Fluidmaster 502 Adjustable Flapper | Best Overall | ~$8 |
| Korky 100BP Universal Flapper | Best Universal Fit | ~$6 |
| Fluidmaster 5403 3-Inch Flapper | Best for 3-Inch Flush Valves | ~$10 |
Best Overall: Fluidmaster 502 Adjustable Toilet Flapper
Fluidmaster is the brand I keep in my truck. The 502 is adjustable — meaning you can control how long it stays open after a flush, which directly affects how much water you use per flush. It fits most 2-inch flush valves and is compatible with American Standard, Kohler, Eljer, and most other major brands.
The rubber compound Fluidmaster uses resists chlorine and mineral buildup better than generic flappers. I’ve had these last 5+ years in hard water areas where cheaper flappers fail in 18 months.
- ✅ Adjustable flush volume
- ✅ Fits most 2-inch flush valves
- ✅ Chlorine-resistant rubber
- ✅ Works with most major brands
- ❌ Doesn’t fit 3-inch flush valves (get the 5403 for those)
Best Universal Fit: Korky 100BP Universal Flapper
If you’re not sure what toilet brand you have or you just want the most universally compatible option, Korky’s 100BP is the standard. It’s been the go-to universal flapper for decades. The flexible design conforms to slightly different valve seat shapes, which is why it seals even on older or non-standard toilets.
- ✅ Fits virtually any 2-inch flush valve
- ✅ Seals well on older toilets
- ✅ Cheap and widely available
- ❌ Fixed flush volume — no adjustment
Best for 3-Inch Flush Valves: Fluidmaster 5403 Flapper
Many newer toilets — Kohler’s Class Five and some American Standard models — use a 3-inch flush valve instead of the standard 2-inch. If you see a large tower-style flush valve in your tank, you need a 3-inch flapper. The Fluidmaster 5403 is specifically designed for these and won’t fail the way a universal flapper will if it’s the wrong size.
- ✅ Made for 3-inch flush valves
- ✅ Strong seal on high-volume flush systems
- ✅ Durable Fluidmaster quality
- ❌ Only for 3-inch valves — check before buying
How to Replace a Toilet Flapper
- Shut off the water supply valve behind the toilet (turn clockwise).
- Flush to empty the tank.
- Unhook the flapper ears from the flush valve pegs and disconnect the chain from the flush lever.
- Hook the new flapper ears onto the valve pegs. The ears should snap securely into place.
- Connect the chain to the flush lever — leave about 1/2 inch of slack.
- Turn the water back on and let the tank fill.
- Flush once. The flapper should seal completely and the water should stop running within 30 seconds of filling.
Plumber’s tip: If the toilet is still running after replacing the flapper, the problem may be the fill valve, not the flapper. Check whether water is flowing into the overflow tube — if it is, your fill valve needs adjustment or replacement.
FAQ
How do I know if my toilet has a 2-inch or 3-inch flush valve?
Open the tank lid and look at the flush valve at the bottom. If the opening (the hole the flapper covers) is roughly the size of a tennis ball, it’s 2-inch. If it’s closer to a baseball, it’s 3-inch. When in doubt, bring the old flapper to the hardware store to match it.
How long should a toilet flapper last?
A quality flapper lasts 5–8 years in normal conditions. Chlorine tablets in the tank dramatically shorten flapper life — if you use those blue tablets, expect to replace the flapper every 1–2 years.
My toilet randomly runs for a few seconds. Is that the flapper?
Yes — this is called “phantom flushing” and it almost always means the flapper is leaking slowly. Water drains from the tank until the fill valve kicks on to refill it. Replace the flapper and it’ll stop.
Bottom Line
Grab the Fluidmaster 502. It’s the most reliable 2-inch flapper on the market, and the $8 you spend will save hundreds on your water bill. If you have a 3-inch valve, get the 5403. Either way, this is a 5-minute fix you can do today.