COMPATIBILITY FIRST · NO INTRO ADS
Replace a 2-inch flush valve
Fluidmaster K-507A-008 adjustable 2-inch flush-valve kit in a compatible two-piece gravity toilet using the standard red tank-to-bowl gasket arrangement. This repair removes the tank.
- Verify a 2-inch flush opening and removable tank before buying.
- Identify the existing gasket shape. This animation uses the kit's red standard gasket; Kohler and Gerber follow different orders.
- The adjustable overflow top must remain at least 1 inch below the bottom of the handle opening.
- The retained fill valve's C.L. mark must remain at least 1 inch above the new overflow opening.
The animation illustrates the named mechanism. Use your exact fixture and replacement-part instructions if their design or sequence differs.
01 / DIAGNOSE BEFORE BUYING
Confirm the repair fits the problem.
- If water leaks into the bowl, first check the chain, flapper condition and clean sealing seat; a flapper-only repair may be sufficient.
- Replace the valve body when the seat or overflow is damaged, or a verified valve-body/seal leak remains after correct flapper repair.
- A tank-to-bowl leak only during flushing can be the large gasket rather than the whole valve.
This procedure does not cover
- 3-inch or larger outlets
- One-piece, pressure-assisted, concealed, dual-flush or proprietary canister toilets
- Kohler and Gerber gasket arrangements, which need the kit's separate illustrated branch
- Any tank whose bolt or gasket layout differs from the illustrated standard layout
02 / COMPATIBILITY & PREPARATION
Have the matching parts ready.
- K-507A-008 kit and verified matching gasket/hardware
- Included red wrench and adjustable pliers
- Screwdriver matching the bolt heads
- Bucket, sponge, towels and a stable padded work surface
- Ruler; scissors if the refill hose needs shortening
These checks are for your use. They do not certify compatibility and are not saved.
03 / STRAIGHT TO THE REPAIR
See how the parts move.
Read the narration transcript
Shut off the water, flush, verify the tank cannot refill, and sponge it dry. This example uses the Fluidmaster adjustable two-inch valve in a compatible two-piece gravity toilet. Disconnect the supply, chain and refill clip. Support the tank, remove its bolts and lift it onto a padded surface. Stop for cracked porcelain or seized hardware. Remove the old gasket, locknut and valve. Clean the seat. Fit the new valve and keep its overflow clear of bolt holes. Adjust and lock the overflow at least one inch below the handle opening. Check the fill valve's C.L. mark stays at least one inch above it. Follow the kit's exact gasket and washer order. For the standard red gasket, tighten the valve nut by hand, then only another half-turn. Cover it fully with the gasket. Refit the tank with rubber washers beneath bolt heads. Tighten both sides evenly until stable, without straining porcelain. Reconnect the chain with about half an inch of slack, clip the refill tube above the overflow, and reconnect the supply. Fill and flush repeatedly. If any joint leaks, shut off and reseat it. Never force the nuts tighter.
04 / THE PROCEDURE
Work gently. Check as you go.
- Empty and disconnect Shut off water, flush, verify isolation and sponge dry. Protect the lid. Disconnect the supply at the tank into a bucket, unhook the flapper chain and remove the refill clip.
- Lift the tank safely Support the tank, undo its mounting nuts and lift it from the bowl. Get help if the lift is awkward. Place it on its side on a padded stable surface, keeping pressure off fragile fittings. Do not force seized bolts against ceramic.
- Remove the old valve Remove the large tank-to-bowl gasket, then the flush-valve locknut. Lift out the old valve and clean the sealing surface. Keep the old gasket long enough to verify the correct kit branch.
- Set and fit the new valve Remove the new gasket, nut, friction washer and any packaging beneath the flapper. Seat the valve with its internal seal; point the overflow rearward without covering bolt holes. Twist-unlock, adjust and relock the overflow at least 1 inch below the handle opening.
- Seal beneath the tank For the standard branch, fit the friction washer and locknut below the tank. Hand-tighten, then use the supplied red wrench for another 1/2 turn only. Fit the red tank-to-bowl gasket fully over the locknut. Follow the separate manufacturer branch for any other gasket.
- Reinstall the tank Place a rubber washer under each bolt head inside the tank. Lower the tank onto the bowl, then fit the metal washers and hex nuts below the bowl. Tighten nuts alternately and evenly until the tank is secure and does not rock. Do not overtighten or force ceramic together.
- Reconnect and test Reconnect the chain directly above the flapper with roughly 1/2 inch slack, as specified for this kit. Refit the refill clip above the overflow, verify fill-valve C.L. clearance and hand-connect the supply. Open water, set the proper level below overflow, then test through several flushes.
05 / VERIFY THE RESULT
Check operation and every disturbed joint.
- Check tank bolts, fill-valve connection and tank-to-bowl gasket while filling and during flushing.
- The tank is stable, the handle returns and the flapper closes flat.
- A leak only during a flush: shut off, drain and inspect gasket centering, fit and coverage of the locknut.
- A leak around a bolt: shut off and check washer placement and seating before any gentle even adjustment.
- Running water into the bowl: check flapper seating, chain slack, overflow setting and the body seal.
KNOW YOUR LIMITS
Stop and get qualified help when…
- Tank crack, severely corroded or seized bolts, or an unsafe heavy lift
- Wrong outlet size, incompatible gasket or unfamiliar mounting system
- Cannot achieve both required height clearances
- Any persistent leak; do not chase it by heavy tightening
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MANUFACTURER REFERENCES
Sources & scope.
Written instructions use the manufacturer references below. The 3D illustration is not a manufacturer certification or a substitute for the instructions supplied with your exact model.
- Fluidmaster K-507A-008 full installation manual
- Fluidmaster 400A critical-level and overflow requirements
- Fluidmaster complete-kit leak troubleshooting
Checked October 11, 2026. These are information links, not affiliate links. We do not sell tools or parts.