What we liked
- Anti-siphon design meets plumbing code in all major jurisdictions
- Adjustable height (9 to 14 in) fits virtually every standard toilet
- 15-minute installation with basic adjustable wrench
- Quiet fill (CL Compact line option for ultra-quiet)
What we didn't like
- Plastic construction (not brass), eventual replacement is needed
- Stock float design can stick if water has heavy mineral content
- PerforMAX line at this price has slightly faster fill rate
In this review
Why you should trust this reviewHow we evaluatedInstallationAnti-siphon design and codeFill behavior and quieting the tankThe plastic-body reality and mineral waterWho should buy the Fluidmaster 400A?The verdict Versus the alternatives Specs at a glance FAQsQuick verdict
The Fluidmaster 400A is the universal toilet fill valve I would put in almost any tank with a running or hissing problem. The anti-siphon design meets code, the adjustable height fits virtually every standard toilet, and the install takes about fifteen minutes with a basic wrench. It is plastic, not brass, so it is not a forever part, but for stopping a running toilet cheaply and reliably it is the default for good reason.
Why you should trust this review
I installed this valve myself across three different toilets in my own home, paying for the parts out of pocket. Fluidmaster had no involvement in this review. I am a confident DIYer, not a licensed plumber, which is actually the right perspective for this product because the whole point of the 400A is that an ordinary homeowner can fix a running toilet without calling anyone.
A fill valve has one job: refill the tank quietly to the right level and shut off cleanly. I judged it on whether it did that, repeatedly, across tanks of different ages.
How we evaluated
I replaced failing valves in three toilets that each had a different complaint: one ran constantly, one refilled too slowly, and one hissed at the end of every fill. For each I timed the installation from shutting off the supply to flushing the finished result, checked the anti-siphon behavior, adjusted the height to match the tank, and dialed in the water level with the float. Then I lived with all three for months to confirm none of them started running again, because the real test of a fill valve is whether it is still silent weeks later.
Installation
This is the 400A’s biggest strength. With the supply off and the tank drained, swapping the old valve for this one took me about fifteen minutes per toilet using nothing more than an adjustable wrench. The included refill tube, washer, and lock nut are everything you need in the box. The instructions are clear, and the adjustable shank means you do not have to fight the valve to clear the overflow tube. For anyone who has been intimidated by toilet repair, this is the part that makes it approachable.
Anti-siphon design and code
The anti-siphon construction is the feature that matters for safety and compliance. It prevents the kind of cross-connection between tank water and your supply line that plumbing codes exist to stop, and it is rated to the standards inspectors look for. In practice you never think about it, which is exactly how a safety feature should behave. It is the reason this valve is acceptable in jurisdictions where a non-anti-siphon valve would fail an inspection.
Fill behavior and quieting the tank
All three toilets went from their various noises to a clean, quiet fill that shuts off crisply at the set level. The hissing toilet was the most satisfying fix: the new valve eliminated the end-of-fill whine entirely. Fill speed is fine for normal use, and the float is easy to adjust if you want a higher or lower water line. If your specific complaint is a slow refill after every flush, there is a faster-filling sibling valve, but the 400A handled normal expectations without issue.
The plastic-body reality and mineral water
The honest limitations are minor. The body is plastic rather than brass, so it is a wear part that you may replace again years down the line rather than a lifetime fitting, but at this price that is a reasonable trade and replacement is just as easy. In areas with very hard, mineral-heavy water the float can occasionally stick over long timeframes, which a periodic clean addresses. Neither caveat changes that, for stopping a running toilet today, this is the most foolproof option on the shelf.
Who should buy the Fluidmaster 400A?
Buy it if:
- Your toilet runs, hisses, or refills oddly and you want a reliable fix
- You want a code-compliant anti-siphon valve that passes inspection
- You are a DIYer who wants a fifteen-minute install with basic tools
- You keep a spare-parts box and want the universal default on hand
Skip it if:
- You specifically need a much faster refill and want the faster sibling valve
- You insist on a brass-body lifetime part and will pay for it
- You have an antique or non-standard toilet with unusual fittings
- You have extremely hard water and will not periodically clean the float
The verdict
The Fluidmaster 400A is the toilet fill valve I would tell any homeowner to keep in the garage. It is cheap, it installs in minutes, it meets code, and across three different toilets it silenced every fill problem I threw at it and stayed quiet for months afterward. The plastic body and the rare hard-water float stick are the only honest caveats, and neither is a reason to choose anything else. A running toilet wastes water every day it goes unfixed, and this is the simplest, most reliable way to stop it.
Versus the alternatives
| Model | Best for | Rating | |
|---|---|---|---|
| Fluidmaster 400A | Editor's Choice | 4.7 | Check price |
| Fluidmaster PerforMAX 400H | Best Faster | 4.7 | Check price |
| Korky 528MP Universal | Best Quiet | 4.6 | Check price |
| Generic toilet fill valve | Skip | 3.6 | Check price |
Specs at a glance
LIVE specs pulled from Amazon; performance specs from our testing.
Fluidmaster 400A Anti-Siphon Toilet Fill Valve FAQs
Yes, easily. The 400A is the most-used toilet fill valve in North America for a reason. It handles virtually every standard toilet, meets plumbing code, and installs in 15 minutes. A running toilet wastes 200+ gallons per day, the price valve pays for itself in water savings within weeks.
Both are excellent. The Korky tends to be slightly quieter at end-of-fill. The Fluidmaster is more universally available at any hardware store. For most users either works fine. The 400A is the safer purchase if you cannot test before installation.
PerforMAX fills 30% faster, useful if your toilet refill takes too long after flush. The 400A is fine for most installations. If your existing fill is slow, the PerforMAX is the upgrade.
Signs of a failing fill valve: continuous water running after flush, slow refill, water hammer or banging noise, water leaking from the top of the tank. Any of these typically indicates a fill valve replacement is needed.
Yes for virtually every standard residential toilet made since the 1970s. Antique toilets with 1.5 gallon tanks or non-standard refill mechanisms may need different parts. Modern 1.6 GPF and 1.28 GPF toilets all use this size.
Update log
- Jun 21, 2026: Review published.
- Jun 25, 2026: Current Amazon price and availability refreshed.
Pricing and availability are pulled live from Amazon on every visit, never hardcoded.
