Tank Fit

Rebuild

Whole rebuild, or just the part that failed?

A fill valve is about $12. A fill valve plus flapper kit is about $20. A full rebuild that includes the flush valve is $30–$40 and requires lifting the tank off the bowl. The right answer depends on the age of the parts and whether the flush valve seat is still good.

Three tiers, plainly

Tier 1 — one part, 15 minutes, no tank removal

Replace the flapper, or replace the fill valve. Correct when one thing failed, the rest is under five years old, and the flush valve seat is smooth.

Tier 2 — fill valve + flapper kit, 25 minutes, no tank removal

The default when both parts are the same age and that age is over five years, or when your water is hard or chloraminated. You are already draining the tank; the second part costs a few dollars and saves you doing this again next spring.

Tier 3 — full rebuild including the flush valve, 60–90 minutes, tank comes off

Required when the flush valve body or its seat is damaged. This means unbolting the tank from the bowl, so it also means new tank-to-bowl bolts and gasket. Budget the extra time and buy the bolts before you start, not halfway through.

Fluidmaster 400AKRP10 / complete-repair class kitFill valve + flapper repair kittypically $18–$25
Fits
Standard two-piece tanks with 2-inch flush valves and 9 in or more floor-to-overflow height. The pragmatic Tier 2 buy.
Does not fit
3-inch flush valve toilets (buy a 3-inch kit), Kohler canister systems, TOTO G-Max, flapperless towers, and short one-piece tanks.
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Korky 4010PK / complete repair class kitFill valve + flapper + hardware kittypically $20–$28
Fits
Same standard tanks. Korky kits commonly include the tank-to-bowl hardware, which is worth having if the bolts are rusted.
Does not fit
Same exclusions. Also confirm 2-inch vs 3-inch on the box — both exist under similar names and the packaging difference is easy to miss at 11pm.
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Six decision rules

  1. Flush valve seat gritty, scored, or cracked → Tier 3. No flapper fixes a bad seat, and you will otherwise buy three flappers before accepting it.
  2. Weeping at the tank bolts or between tank and bowl → Tier 3. The tank has to come off anyway; do the flush valve while it is on the towel.
  3. Both parts over 5 years old → Tier 2. Cheaper in labor-hours than two separate evenings.
  4. Hard or chloraminated water → Tier 2 minimum, with silicone rubber. See hard water.
  5. Kohler Class Five or TOTO G-Max → do not buy a universal kit. Replace the specific seal. See Kohler and TOTO.
  6. Toilet is pre-1994 and uses 3.5 gpf or more → consider replacing the toilet. A rebuild on an old water hog is fine and cheap, but if you were already thinking about it, the water math favors a 1.28 gpf WaterSense-labeled unit. The EPA WaterSense specification is public and worth reading before you spend on a rebuild you may throw away in a year.

Tank removal: two things that go wrong

Rusted tank bolts. If the nut will not move, do not muscle it — you will crack the tank. Cut the bolt with a hacksaw blade or an oscillating tool, protecting the china.

Setting the tank back down. Tighten the tank bolts alternately, a little at a time, until the tank is snug and level. Vitreous china does not flex; over-torquing one side is how you get a hairline crack that shows up as a puddle a month later.

What a full rebuild does not fix

  • Water at the base of the toilet — that is the wax ring or the flange.
  • A weeping shutoff or a crusty supply line.
  • A bowl that clogs on normal use — that is trapway or drain, not tank hardware.
  • Noise transmitted through the wall framing. See quiet fill.

Order of operations for a Tier 3 evening

  1. Buy the kit, tank-to-bowl bolts, and a new supply line before you start.
  2. Close the stop, flush, sponge dry, disconnect the supply.
  3. Unbolt the tank, lift it onto a towel, remove the old flush valve nut.
  4. Install the flush valve with its cone washer inside the tank, snug not brutal.
  5. Install the fill valve, set the height, then the flapper and chain.
  6. New tank-to-bowl gasket, reset the tank, alternate the bolts.
  7. New supply line, open the stop slowly, dye test in fifteen minutes.

Next, in the tank