The fill valve is the vertical column on the left side of the tank — it refills the tank after each flush. TOTO Drake-series and most other tank-style TOTOs use a standard Fluidmaster-pattern fill valve, meaning replacement is straightforward with universal aftermarket parts. Service life is typically 7–10 years; failures show up as whistling, slow fill, or no shutoff.
How to identify your TOTO fill valve
Lift the tank lid. The fill valve is the vertical plastic column with a float on the side or a cup float on top. TOTO uses two fill-valve patterns:
- Standard Fluidmaster-pattern (most Drake-series, UltraMax II, Vespin II) — cup-style float that slides up and down a center post. Fluidmaster 400A is a direct drop-in replacement.
- TOTO Premier fill valve (Aquia IV dual-flush, some Carlyle II) — TOTO's proprietary fill mechanism with a hidden internal float. Fluidmaster 400A fits as a swap but the dual-flush integration may need TOTO-specific replacement.
Failure symptoms
- Whistling or "singing" during refill — mineral buildup inside the valve causing turbulent water flow. The most common TOTO fill-valve symptom in hard-water areas.
- Slow fill — refill takes 90+ seconds. Valve orifice partially clogged with sediment.
- Fill valve doesn't shut off cleanly — water trickles past the float-stop point. Tank overflows into the overflow tube, the fill valve runs continuously.
- Water level set wrong — float position incorrect, or float has cracked and is sitting too low/high.
Replacement parts
- Fluidmaster 400A (universal) — $10–$15. Fits all Drake-series TOTOs and most UltraMax. The volume aftermarket pick.
- Fluidmaster 400AKR Pro Series — $15–$20. Quieter operation, less mineral-buildup susceptibility. Recommended for hard-water areas.
- Korky 528MP (universal) — $10–$15. Korky's universal fill valve. Comparable to Fluidmaster 400A.
- Korky 818 PerforMAX — $20. Self-cleaning fill valve — periodically backflushes sediment. Best for high-sediment water supplies.
- TOTO TSU01W.10R (OEM fill valve for Drake series) — $25–$35. Genuine TOTO. Worth it if matching original equipment matters; otherwise functionally equivalent to Fluidmaster 400A.
- TOTO TSU99A.X (OEM fill valve for Aquia IV dual-flush) — $45. TOTO-specific dual-flush integration; not interchangeable with universal valves.
Replacement procedure (20 minutes)
- Shut off water at the wall, flush, sponge dry the tank.
- Disconnect the supply line at the bottom of the tank (small adjustable wrench).
- From inside the tank, unscrew the large plastic locking nut at the base of the fill valve.
- Lift the old fill valve out.
- Insert the new fill valve from inside the tank. Screw on the locking nut from below (finger-tight + 1/4 turn).
- Reconnect the supply line — 7/8" UNF threading is universal across all US fill valves and TOTO tanks.
- Adjust the water level (float setting on the new valve). Target: 1 inch below the top of the overflow tube.
- Turn water on. Check for leaks at the supply connection and the locking nut.
Adjusting the water level on a new fill valve
- Fluidmaster 400A: twist the small screw on top of the valve clockwise for higher water level, counter-clockwise for lower.
- Korky 528: squeeze the clip on the float arm and slide the float up or down.
- TOTO TSU01W: rotate the float-position screw on the side.
Mark your target water level inside the tank with a Sharpie for future reference. The standard is 1 inch below the top of the overflow tube.
The TOTO-specific fill-valve consideration
TOTO Drake-series tanks have a slightly taller-than-average fill-valve well, which means short fill valves can occasionally not seal properly against the tank bottom. The Fluidmaster 400A and Korky 528 are both tall enough to fit; some generic-brand fill valves under $8 are too short. Stick with the named brands.
Cost summary
- Fluidmaster 400A: $10–$15
- DIY time: 20 minutes
- Tools: adjustable wrench, sponge
- Plumber service call: $180–$280