Toilet Tank Parts: Every Part Named and What It Does

Toilet tank parts come down to about a dozen named pieces: the fill valve and float, refill tube, overflow tube, flush valve, flapper, chain, handle, gasket, bolts, supply line and shutoff.

What are the parts of a toilet tank?

The parts of a toilet tank split into two groups. Inside the water sit the fill valve, its float cup, the refill tube and clip, the overflow tube, the flush valve, the flapper, the lift chain and the trip lever. Outside or under the tank sit the handle, the tank-to-bowl gasket, two or three tank bolts, the supply line and the shutoff valve.

The diagram below labels each one where it sits in a standard two-piece gravity tank. For the sequence of what happens when you push the handle, read our explainer on how a toilet works from flush to refill.

Diagram by The Plumbing Brief. Water line, cap height and overflow clearance follow the Fluidmaster 400H instructions. Not to scale.

What does each toilet tank part do, and how does it fail?

Each toilet tank part has one job and one or two predictable ways to fail. The table maps every part to its function, the symptom you notice, a typical replacement part and its price. Prices come from Fluidmaster’s own online store in October 2026, before shipping and tax, unless noted.

How do the fill valve, float and refill tube work together?

The fill valve, float cup and refill tube form one assembly on the left side of most tanks. When the tank empties, the float cup drops and opens the valve. Water refills the tank while the refill tube sends a smaller stream down the overflow tube into the bowl. When the float reaches its set height, the valve shuts.

The Fluidmaster 400H PerforMAX is the common universal replacement. Its install guide runs eight steps, needs only a bucket, sponge, towel and optional scissors, and ships with the refill tube, clip, shank washer and locknut. Fluidmaster backs it with a limited seven-year warranty.

1. Close the shutoff valve clockwise, flush, and sponge out the remaining water.
2. Unscrew the supply connector and old locknut, then lift out the old valve.
3. Twist the new valve body until the top of the cap sits roughly 3 inches above the top of the overflow pipe. Do not move the lock ring.
4. Drop the valve in, clip the refill tube to the overflow pipe, and hand tighten the locknut.
5. Reattach the supply connector by hand, open the water and check for leaks.

Steps follow the Fluidmaster 400H quick install guide. If the valve later will not shut off, Fluidmaster’s fix is to flush grit out under the cap or fit a 242 seal. Our toilet fill valve guide compares float-cup, ballcock and floatless designs.

How high should the water be in a toilet tank?

Fluidmaster’s 400H instructions put the tank water roughly 1/2 inch below the top of the overflow pipe and say the setting “does not need to be exact.” Higher and water spills down the overflow tube, so the toilet runs. Turn the adjustment screw clockwise to raise the level, counterclockwise to lower it.

Three heights in the tank all reference the overflow pipe. The water line sits about 1/2 inch below it. The fill valve’s critical level (CL) mark sits above it; Fluidmaster’s 400A instructions require the CL mark 1 inch above the overflow pipe and call that a plumbing code requirement. And the top of the overflow pipe must sit at least 1 inch below the handle hole in the tank wall.

If your tank has a molded water line from its maker, use it over any rule of thumb. The 400H also has a bowl water level dial, preset for most toilets; Fluidmaster’s check is to pour a gallon into the bowl, wait one minute, pencil the line, then flush and match it.

What size flush valve and flapper does a toilet tank take?

Toilet tank flush valves come in three size classes: 2 inch, 3 inch and 4 inch. Fluidmaster says most toilets built before 2005 take a 2 inch flapper. Measure the drain hole under the flapper. Fluidmaster puts it at about 2.5 inches for a 2 inch flapper and about 3.5 inches for a 3 inch flapper. Some 4 inch valves, such as the American Standard Champion 4, use a seal instead of a hinged flapper.

Sizes and the pre-2005 rule come from Fluidmaster’s guide to telling a 2 inch from a 3 inch flush valve, and Korky’s flapper sizing page walks through the same measurement. See how a toilet flapper seals and wears out for rubber types.

Chain length matters as much as size. Fluidmaster’s 400H troubleshooting page calls for about 1/2 inch of chain slack.

Which toilet tank parts sit outside or under the tank?

Five parts sit outside the water: the handle, the tank-to-bowl gasket, the tank bolts, the supply line and the shutoff valve. They fail less often than the flapper, but their leaks land on the floor instead of in the bowl.

• Handle. The mounting nut inside the tank is reverse threaded on most toilets, so it tightens counterclockwise. A Perfect Fit lever runs $15.99 to $16.99.
• Tank-to-bowl gasket. The thick gasket around the flush valve outlet; replacing it means lifting the tank off.
• Tank bolts. Usually two or three, each with a rubber washer inside the tank and a metal washer and nut below. Tighten them evenly and stop at snug, since Fluidmaster’s gasket instructions warn that overtightening can crack the bowl.
• Supply line. Fluidmaster tells 400H installers to replace the connector if it is worn or of unknown age. Its Click Seal line sells for $11.99 to $13.99.
• Shutoff valve. Turn it clockwise to close. If it will not close fully, replace it before any tank repair.

How much do toilet tank parts cost?

Single toilet tank parts cost $9.48 to $18.99 on Fluidmaster’s own store in October 2026, and its fill valve and flapper kit costs $28.99. The cheapest items are the 510A and 510K canister seals; the priciest single part is the 400H fill valve. Complete repair kits run $29.99 to $34.99.

Prices are the starting price for each listing on the Fluidmaster online store, checked October 2026, before shipping and tax.

Buying the 400H and Super Flapper separately costs $35.98, so the $28.99 kit saves $6.99 and one tank draining.

How do you tell which toilet tank part is failing?

Run two checks before buying anything. First, the EPA dye test: add a few drops of food coloring to the tank, and if color shows up in the bowl after 10 minutes, the flapper or flush valve seat is leaking. Second, watch the overflow tube during a refill. Water pouring into it points to the fill valve or its level setting.

1. Color in the bowl. Flapper or flush valve seat. Replace the flapper first.
2. Water running down the overflow tube. Level too high or fill valve not shutting. Lower the level, then fit a 242 seal or new valve.
3. Tank fills, bowl stays low. Refill tube off the overflow pipe or clipped wrong. Fluidmaster says the metal side of the clip faces out.
4. Weak flush, flapper drops early. Chain slack off or water too low. Reset to 1/2 inch of chain slack and 1/2 inch below the overflow top.
5. Drip under the tank. Gasket, bolt washers, locknut or supply line.

EPA WaterSense says the average household’s leaks waste more than 9,300 gallons a year per its Fix a Leak Week page. For the full step-by-step on the two most common faults, see how to fix a running toilet.