COMPATIBILITY FIRST · NO INTRO ADS
Rebuild the tank internals
Fluidmaster 400ARHRK PerforMAX all-in-one kit in a compatible two-piece gravity toilet with a 2-inch flush outlet, two mounting bolts and standard tank-to-bowl gasket. Manufacturer positions this kit for 1.6 gallons per flush or less.
- Confirm a conventional 2-inch, two-piece tank and the correct standard gasket before disassembly.
- Kit washer order differs from the standalone adjustable flush-valve kit; do not mix the two diagrams.
- The new fixed overflow must be cut outside the tank to the manual's height, 1 inch below the handle opening.
- Keep the fill valve's C.L. mark at least 1 inch above the overflow and preserve lid/float clearance.
- Do not move the fill-valve lock ring, mix an old shank with the new valve, or add bleach/chlorine drop-in tank cleaners.
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.
- A full rebuild is appropriate when several compatible tank components are worn or leaking, or the tank must already come off for a damaged flush valve.
- One disconnected chain, dirty fill-valve seal or worn flapper does not by itself require a whole-tank rebuild.
- A crack or toilet-base/floor leak is a different repair; do not expect an internals kit to fix it.
This procedure does not cover
- One-piece, pressure-assisted, tankless, concealed, dual-flush, electronic or specialty flushing systems
- 3-inch flush outlets
- Gerber and Kohler tanks needing separately specified tank-to-bowl gaskets
- Three-bolt tanks unless the exact extra hardware and manufacturer procedure have been confirmed
- Side-entry fill valves or proprietary handles
02 / COMPATIBILITY & PREPARATION
Have the matching parts ready.
- 400ARHRK kit with all seals, bolts, washers and nuts checked against its parts list
- Compatible supply connector if the old one is worn or over five years old
- Adjustable pliers and matching screwdriver
- Bucket, sponge, towels and stable padded work surface
- Ruler, pencil, scissors and mini hacksaw for the fixed overflow if needed
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, and verify the tank cannot refill. Sponge it dry. Use this rebuild only for the compatible two-piece, two-inch tank shown. Check the kit and gasket first. Disconnect the supply, then remove the fill valve, chain and handle. Support and unbolt the tank; lift it onto a padded surface. Stop for cracks, seized bolts or an unsafe lift. Remove the old gasket and flush valve. Set the new overflow one inch below the handle opening; make any required cut outside the tank. Fit the valve and matching gasket using the kit's exact washer order and tightening limits. Refit the tank and tighten its bolts evenly, without straining porcelain. Install the fill valve with its C.L. mark at least one inch above the overflow. Hand-tighten its nut. Fit the handle, leave half an inch of chain slack, and clip the refill tube above the overflow. Reconnect the supply by hand. Turn on, set the correct water level below overflow, and adjust the flapper and refill flow. Flush several times. Every joint must stay dry and the valve must shut off. For leaks, shut off and correct the seals; do not force tighter.
04 / THE PROCEDURE
Work gently. Check as you go.
- Isolate and strip Protect the lid and note the proper water level. Shut off, flush, verify isolation and sponge dry. Disconnect the supply. Remove the fill valve, refill tube, flapper chain and reverse-thread handle nut/lever.
- Remove the tank Support the tank, undo its mounting nuts and lift onto a padded stable surface. Remove the old bolts, large gasket and flush-valve nut, then withdraw the old valve. Clean sealing areas and inspect for cracks.
- Prepare the flush valve Trial-fit the new valve without its external nut/gasket, mark its overflow 1 inch below the handle opening, then remove it to cut if required. Clear debris before refitting. Keep the overflow toward the rear and bolt holes unobstructed.
- Seal the outlet Seat the internal valve gasket. Tighten its large locknut by hand plus 1/2 turn, following this kit's manual. Fit the matching tank-to-bowl gasket fully over the nut. Do not substitute the supplied standard gasket on a tank requiring another shape.
- Fit bolts and replace tank Put a rubber washer beneath each bolt head inside the tank. For the illustrated basic two-bolt installation, omit the optional reinforcing nuts below the tank. Lower tank onto bowl. Below the bowl, fit rubber washer, metal washer and hex nut to each bolt. Tighten alternately until stable without overtightening. If using the optional reinforcing arrangement, follow the manual and ensure its thin nuts never contact bowl porcelain.
- Install fill valve and handle Fit the fill-valve shank washer flat side against the valve. Set C.L. at least 1 inch above the overflow and hand-tighten the lower locknut; keep the float clear. Install the front-mount lever and its reverse-thread nut, then connect the chain directly above the flapper with the kit's specified 1/2 inch slack.
- Connect refill and supply Fit the refill tube, roller clamp, hose clamps and clip as supplied. Clip its discharge above the overflow; never insert it below the tank water line. Reconnect the correctly sealed supply coupling by hand.
- Tune and leak-test Open water and check all joints. Set tank water to the toilet's specified line below overflow; this kit recommends about 1/2 inch clearance. Adjust flapper duration and bowl-refill clamp per the manual, then flush repeatedly. Check leaks both at rest and during flushing before replacing the lid.
05 / VERIFY THE RESULT
Check operation and every disturbed joint.
- No moisture at supply, fill-valve shank, mounting bolts or tank-to-bowl connection.
- Stable tank, free-moving float, returning handle and fully seating flapper.
- For low bowl water, check the refill path and increase refill-clamp flow as required; for a weak flush, verify tank level and flapper setting.
- For refill noise when unused, locate tank leakage; for failure to stop filling, isolate supply and follow the fill-valve cleaning procedure.
- For a flush-only leak, inspect gasket fit/centering after shutting off and draining.
KNOW YOUR LIMITS
Stop and get qualified help when…
- Shutoff failure or leak
- Cracked ceramic, seized hardware or unsafe tank lift
- Wrong kit, outlet, gasket or washer layout
- Inability to obtain critical-level, overflow or lid clearance
- Persistent leakage or a tank that stays unstable without excessive 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 400ARHRK installation manual, revision 2
- Fluidmaster 400ARHRK detailed troubleshooting, revision 1
- Fluidmaster manufacturer video: 400ARHRK scope
- Fluidmaster PRO45K installation: related complete-kit safety and flushing
Checked October 11, 2026. These are information links, not affiliate links. We do not sell tools or parts.