Replacing a Toilet Flapper Takes Ten Minutes and Two Trips

The toilet in the hall bathroom was refilling itself for about four seconds every twenty minutes, all night long, like it had just remembered something. My wife asked at 2 a.m. whether it was supposed to do that. It wasn't. She was right, as she usually is about noises.

That sound is almost always the flapper. A universal one runs roughly five to fifteen dollars. The job takes ten minutes once you're holding the right part, and the "once" is doing a lot of work in that sentence.

What the box says

"Fits most toilets. Installs in minutes. No tools required."

What you will actually need

• A new flapper. Universal models from Fluidmaster or Korky cover a lot of toilets for roughly $5 to $15. Some Kohler, Toto and American Standard toilets use their own seals, which cost more and live in a smaller section of the aisle.
• Your old flapper in a zip-top bag. This is the thing everybody forgets. Bring it to the store.
• The toilet's model number. It's usually stamped inside the tank on the back wall, sometimes below the waterline. Take a phone picture.
• A sponge and an old towel.
• Rubber gloves. Optional, technically.
• Food coloring. For the diagnosis, and again for the victory lap.
• A nonscratch scrub pad.
• Scissors or wire snips for trimming the chain.
• A flashlight, because the inside of a tank is darker than you'd expect from a white box.

"No tools required" is honest. You just need everything else on this list.

The steps

1. Confirm it's the flapper. Lift the tank lid and set it flat on a folded towel on the floor. Porcelain lids crack if you lean them on the seat or the edge of the sink. Look at the overflow tube, the open pipe standing in the middle of the tank. If water is spilling into the top of it, your problem is the fill valve set too high, not the flapper. If not, put ten drops of food coloring in the tank and walk away for twenty minutes without flushing. Color in the bowl means the flapper is leaking.

Telling the family "nobody flush" works for about six minutes. Put a sticky note on the lid.

1. Shut off the water. Turn the supply valve behind the toilet clockwise until it stops. If it won't budge or starts to leak, don't force it. Shut off the main water to the house instead. Then flush and hold the handle down to drain the tank.

1. Sponge out the last inch of water. Wring it into a bucket. The tank never fully drains, and the flapper ears sit right in what's left.

1. Unclip the chain and take off the old flapper. Unhook the chain from the handle arm. Most flappers pop off two small pegs on either side of the overflow tube. Others have a rubber ring that slides up and over the tube.

If the old flapper feels like a gummy bear that's been in a hot car, you've found your leak. The bleach tablets you drop in the tank speed that along. Flapper makers warn against them for a reason.

1. Go to the store. Take the bag and the photo. Most flush valves are 2 inches across, but plenty of newer toilets use 3-inch valves, and the two don't swap. Measure the opening if you're unsure.

The guy in aisle nine will tell you they're all the same. With love, they aren't.

1. Clean the flush valve seat. That's the ring at the bottom of the tank where the flapper sits. Wipe it with the nonscratch pad until it's smooth, then run a fingertip all the way around. You're feeling for mineral crust, nicks or pitting. A new flapper on a rough seat leaks just like the old one did.

1. Install the new flapper. Hook the ears over the pegs, or slide the ring down over the tube. Universal flappers often come with both. Cut off whichever one you aren't using so it doesn't get in the way. If yours has an adjustment dial, set it to the gallons-per-flush number stamped on the toilet, often 1.6.

1. Set the chain. Clip it to the handle arm with about half an inch of slack when the flapper is closed. Trim the extra, leaving a link or two of spare. Long chain tails get pinned under the flapper and hold it open.

This step takes four tries. Every time. Nobody has ever gotten the chain right on the first one.

1. Turn the water back on slowly. Open the supply valve counterclockwise and let the tank fill. Check the valve for drips, flush three times, then repeat the food coloring test. Clear bowl after twenty minutes means you're done.

Leave it better than you found it. Wipe down the tank rim, rinse the lid and put it back where it belongs.

Where it goes wrong

It still runs. Check the chain first. Too tight, and the flapper can't seal. Bump the clip one link looser. If the chain's fine, look at the water level again. It should sit about an inch below the top of the overflow tube, and many tanks have a line marking the spot. If it's higher, adjust the float on the fill valve so it shuts off lower.

The flush is weak or quits halfway. That's usually too much chain slack, so the flapper drops before the tank empties. Tighten it a link. On an adjustable flapper, turn the dial toward a longer open time. If the bowl is draining slowly instead of flushing weakly, that's a clog, and a different job: unclog a drain with a plunger, a snake and ten minutes.

New flapper, same leak. The seat is damaged. Seat repair kits glue a fresh ring over a pitted valve and are worth a shot. If that fails, the flush valve itself needs replacing. That means taking the tank off the bowl, which is a bigger Saturday.

Same rule as most repairs in this house: check the cheap part first. It applies to a dishwasher that won't drain too.

When to call a pro

Call a licensed plumber if the supply valve won't shut off, leaks after you turn it back on, or crumbles in your hand. Old multi-turn valves do that. Call one if there's water on the floor around the base of the toilet, which usually means the wax ring, or if you spot a crack anywhere in the tank or bowl. A cracked tank can let go without warning.

Replacing a flush valve is doable for a patient homeowner. Replacing the whole toilet or the shutoff valve is where a lot of people sensibly hand it off. Codes on supply lines, shutoff valves and fixture replacement vary by area, and so do the rules on what a homeowner can do without a permit. Check with your local building department if you're unsure.

You'll know you got it right at 2 a.m. Nothing happens.