Fluidmaster 502 / Korky 100BP
Replace a 2-inch toilet flapper so the tank stops leaking into the bowl
The flapper is the rubber seal at the bottom of the tank that lifts when you flush. A worn one lets water seep into the bowl, so the fill valve keeps topping the tank up. EPA says to check it periodically and replace it at least every five years. Most two-piece toilets use the 2-inch size.
- Drain openingabout 2.5 in
- Old flapper acrossabout 3 in
- Chain slackabout 1/2 in
- Replaceat least every 5 years (EPA)
Is yours a 2-inch flapper?
Flush valve size is set by the hole the porcelain maker bored through the bottom of the tank, so measure rather than guess.
- Drain opening about 2.5 inches across: 2-inch flapper.
- Old flapper about 3 inches from end to end: 2-inch flapper.
- Does it look like a tall cylinder or a tower instead of a hinged rubber disc? You have a Kohler canister or an American Standard Champion 4, and need a different part.
Not sure? Measure the other way too: the 3-inch flapper guide covers the other size.
Which flapper to buy
- Fluidmaster 502
- PerforMAX adjustable 2-inch flapper with a solid frame and a dial. Fits most 2-inch flush valves, rated for 1.28, 1.6 and 3.5+ gallon toilets, five-year warranty. For toilets made 1950 to 1984, Fluidmaster recommends its non-adjustable 501 instead.
- Korky 100 (also sold as 100BP)
- Korky's 2-inch Ultra High Performance flapper: adjustable, stainless steel chain, rated for 1.28 to 5 gallon toilets, five-year warranty. 100BP is an alternate part number for the same flapper.
- Fluidmaster 523A
- The Super Flapper, which Fluidmaster says replaces both 2-inch and 3-inch flappers.
Fluidmaster's rule of thumb: adjustable flappers are for 1.28 and 1.6 gallon toilets (1994 onward); non-adjustable ones are for older 3.5 gallon and larger toilets. A flexible-frame model (Fluidmaster 503, 504 or 5051) helps when the back half of the old flapper did not seal, or on oval overflow pipes and angled seats.
| Item | Part | Number |
|---|---|---|
| 1 | 2-inch flapper on the flush valve seat | Fluidmaster 502 / Korky 100BP |
| 2 | Overflow pipe with mounting posts | part of the flush valve |
| 3 | Lift chain | comes with the flapper |
| 4 | Tank lever arm | reuse |
Check the maker's fit list against your toilet model before buying.
Tools and supplies
- Sponge and towel
- Clean cloth for the seat
- Food coloring for the dye test
- Scissors or pliers to trim chain
Replace the 2-inch flapper
Close the stop valve behind the toilet and empty the tank
Turn the stop valve on the wall or floor behind the toilet clockwise until it is snug. Flush and hold the handle down to drain the tank, then sponge out the water left in the bottom. If the tank starts refilling, the stop is not holding.
Safety: Do not force a stop valve that will not turn; old stops can break or start leaking at the stem. Use the house main instead.
Measure to confirm the size
With the tank empty, measure the drain opening the flapper covers. Fluidmaster: an opening of about 2.5 inches takes a 2-inch flapper, about 3.5 inches takes a 3-inch. Or measure the old flapper end to end: about 3 inches across is a 2-inch flapper, about 4 inches is a 3-inch. Yours should be about 2.5 inches and 3 inches.
Unhook the chain and remove the old flapper
Unclip the chain from the tank lever. Unhook the flapper's arms from the mounting posts on the overflow pipe, or lift them off if it has a solid frame. Take it with you if you are buying the part today.
Clean and feel the seat
Wipe slime and grit off the flush valve seat with a clean cloth, then run a finger around the rim. A nick, chip or rough patch there will leak under any flapper and means the flush valve needs repair or replacement.
Fit the new flapper
Remove any cardboard packing from under the new flapper. Set it on the seat and snap its arms onto the mounting posts. Lift and lower it by hand: it should drop squarely onto the seat and move freely.
Attach the chain with a little slack
Clip the chain to the hole on the tank lever directly above the flapper. Fluidmaster's guide is about 1/2 inch of slack with the flapper closed, a small J shape. Too tight holds the flapper off its seat; too loose gives a weak flush or lets the chain get caught under the flapper. Use the old chain length as a guide and cut off spare chain that could tangle.
Turn the water on and tune the flush
On the Fluidmaster 502 the dial comes set to its maximum, 9. Higher numbers keep the flapper open longer. Flush, then turn the dial down one number at a time until the toilet no longer clears paper properly, and go back up one. On the Korky 100, turn the numbered band.
Dye-test it
With the tank full, add a few drops of food coloring and do not flush. If color appears in the bowl after 10 minutes, the flapper or seat is still leaking: recheck the chain and seat. Flush when you are done so the dye does not stain.
Stop and call a plumber if
- The stop valve behind the toilet will not close, or it drips at the stem or the nut once you have moved it.
- The supply line is corroded, kinked, bulging, or a braided line shows broken strands. Fluidmaster's own sheets say to replace a supply connector that is worn or over five years old.
- Water is on the floor around the base of the toilet, or the floor near it feels soft. That points to the wax ring or flange, which means pulling the toilet.
- Water drips from the tank bolts or between the tank and bowl. Fixing that, or replacing the whole flush valve, means taking the tank off the bowl.
- You see a crack in the tank or bowl porcelain, even a hairline one.
- The flush valve seat itself is chipped or pitted and a new flapper still leaks.
Troubleshooting by symptom
| What you see | Likely cause and fix |
|---|---|
| Dye shows in the bowl after 10 minutes | Flapper not sealing. Check chain slack, clean the seat, feel for nicks. A flapper older than five years: replace it. |
| Toilet refills by itself (ghost flushing) | Water is leaking out of the tank. Check that the refill tube is clipped above the overflow pipe and not pushed into it, then the flapper. |
| You have to hold the handle down to flush | Chain too slack or the dial set too low. Shorten the chain a link or two, or turn the dial up. |
| Weak flush that leaves paper | Dial set too low. Turn it up one number at a time. |
| New flapper warped quickly | Fluidmaster blames chlorine tablets in the tank for warped flappers. Remove them. |
| Still leaks with a new flapper and a clean seat | The flush valve seat or gasket is worn. Fluidmaster's next step is a new flush valve, which means taking the tank off the bowl. |
Official parts and warranty
Fluidmaster gives the 502 a five-year warranty; Korky's 100 carries five years.