Tank Fit

Fill valves

Which fill valve fits: 400A, PerforMAX, QuietFILL, or brass shank

One measurement decides this. Take the tank lid off, put a tape measure on the tank floor, and read the height to the top of the overflow tube. Everything below follows from that number.

Take the measurement first

Every modern fill valve is a plastic tube that telescopes. The number that matters is the distance from the inside floor of the tank to the top of the overflow tube, because the critical-level mark on the valve has to sit at or above that tube — that is what keeps tank water from siphoning back into your supply.

waterlinefill valveflush valve / seatflappersupply line + shutoff
Measure from the tank floor (not the outside bottom) to the top of the overflow tube. Also note whether the shank enters the bottom of the tank or the side.

Write down three things before you go to the store:

  1. Floor-to-overflow-top height, in inches.
  2. Inside tank width at the left side — a tall float cup needs room to travel.
  3. Whether the water enters through the bottom of the tank (almost everything) or through the side (older and some one-piece designs). Side entry is a different valve entirely.

The four honest choices

Fluidmaster 400AAnti-siphon fill valve, adjustable 9–14 intypically $10–$14
Fits
Standard two-piece bottom-entry tanks with 9 in or more of floor-to-overflow height. The default, correct answer for most 1.6 gpf and 1.28 gpf toilets sold in the last 30 years.
Does not fit
Short one-piece tanks that need under 9 in, side-entry tanks, and flapperless pressure/tower designs like many Glacier Bay and Niagara models. See the dedicated does-not-fit page.
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Fluidmaster 400AH / PerforMAXHigh-performance adjustable fill valve, 10–15 intypically $13–$18
Fits
Same standard tanks as the 400A, and taller tanks where the 400A tops out. Fluidmaster's documentation describes it as their higher-flow valve, which helps when the fill takes over a minute — often the case at low household pressure or on a long branch line.
Does not fit
Short tanks (it will not go low enough), and it does not fix a slow fill caused by a half-closed angle stop or a scaled supply line. Check those first, they are free.
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Korky QuietFILL (528 family)Quiet-refill valve, adjustabletypically $12–$18
Fits
Standard bottom-entry tanks where noise is the actual complaint — a bathroom sharing a wall with a bedroom, or a powder room off a hallway. Korky's design routes the refill to run quietly rather than spraying into open air.
Does not fit
It is not a cure for water hammer or singing pipes in the wall — that is a pressure and support problem outside the tank. Same height limits as any telescoping valve.
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Brass-shank ballcockMetal-shank fill valve for old tankstypically $18–$35
Fits
Pre-1990s tanks with a corroded or non-standard opening where a plastic shank will not seal, and cases where you want metal threads on an old, brittle tank. Also the pragmatic pick when the existing nut has already cracked a plastic shank once.
Does not fit
Overkill on any modern tank, heavier and pricier, and it will not help fill speed. Never crank a metal nut onto a vitreous china tank — that is how tanks crack.
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Decision shortcuts

  • Height under about 9 in (typical of low-profile one-piece tanks): skip the universals, look up the OEM valve for your model number.
  • 9–14 in, standard tank, nothing unusual: 400A. Done.
  • Fill is slow and the stop is fully open: 400AH PerforMAX.
  • Noise is the complaint: Korky QuietFILL, and read the quiet fill page for the rest of the noise sources.
  • Old tank, ugly opening, metal nut: brass shank.
  • Kohler Class Five or TOTO G-Max: the fill valve is usually interchangeable, but the flush side is not. See Kohler and TOTO.

Installing it without a second trip

  1. Close the stop, flush, sponge the tank dry.
  2. Unscrew the supply nut, then the shank nut under the tank. Support the tank with your other hand; do not lever against the china.
  3. Set the new valve height so the critical-level mark sits at least an inch above the overflow tube top, then lock it.
  4. Hand-tighten the shank nut, then a quarter turn with the wrench. Plastic nuts seal by gasket compression, not torque.
  5. Reconnect, open the stop slowly, and adjust the float so the water stops about an inch below the overflow top or at the molded mark.
  6. Flush a few times and dry the floor. Any dampness in an hour means the shank gasket, not the valve.

Anti-siphon is not optional

Any replacement fill valve you buy should be anti-siphon rated. It exists so tank water cannot be pulled back into your drinking water if supply pressure drops. The old float-ball ballcocks that lacked it are exactly what plumbing codes moved away from — do not scavenge one from a garage shelf.

Next, in the tank