Few plumbing problems are more annoying than spotting water dripping from under your toilet tank. If your Fluidmaster fill valve is leaking from the bottom, it usually means the seal between the valve and the tank is failing, the locknut is loose, or the plastic shank has cracked. While this may look serious, the good news is that it’s often one of the easiest toilet repairs you can tackle yourself.
In this guide, we’ll explain why Fluidmaster valves leak from the bottom, quick fixes you can try, and the best replacement Fluidmaster valves and kits to stop the problem for good.
Quick Picks: Best Fluidmaster Fill Valves
- Best Overall: Fluidmaster 400AH PerforMAX High-Performance Fill Valve – Quiet, adjustable, and long-lasting.
- Best Budget: Fluidmaster 400A Universal Fill Valve – Reliable, affordable, and easy to install.
- Best Premium: Fluidmaster 400CRP14 Fill Valve & Flapper Repair Kit – Complete repair solution for older toilets.
Why a Fluidmaster Fill Valve Leaks from the Bottom
If you see water dripping where the valve passes through the tank, the problem is almost always one of these:
- Worn-out shank washer: The rubber washer under the tank eventually hardens or cracks, letting water escape.
- Loose locknut: If the nut securing the valve isn’t tight, water can seep around the base.
- Over-tightened nut: Too much torque can warp the washer or crack the shank, causing leaks.
- Cracked valve body: Plastic parts can split over time, especially if exposed to hard water.
- Damaged supply line washer: Sometimes the leak appears to be from the valve but is actually the line below it.
Quick Fixes Before Replacing
- Turn off the water supply and flush the toilet to empty the tank.
- Tighten the locknut gently — snug, but not overtightened.
- Inspect and replace the shank washer if it looks brittle or worn.
- Check the supply line connection and washer for drips.
- If cracks are visible or the leak persists, replace the entire valve.
Detailed Product Reviews: Best Fluidmaster Fill Valves & Kits
1. Fluidmaster 400AH PerforMAX High-Performance Fill Valve
Who it’s for: Anyone who wants a durable, universal replacement that eliminates leaks and improves performance.
- Key Benefits: Adjustable height, fast refill, water-saving design.
- Pros: Quiet operation, fits most toilets, strong sealing at the tank base.
- Cons: Costs a bit more than the basic 400A model.
Final Verdict: The best all-around Fluidmaster replacement for preventing bottom leaks.
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2. Fluidmaster 400A Universal Fill Valve
Who it’s for: Homeowners who need a quick, budget-friendly fix for a leaking valve.
- Key Benefits: Universal fit, simple installation, time-tested design.
- Pros: Inexpensive, reliable, plumber-recommended.
- Cons: No advanced water-saving features.
Final Verdict: A tried-and-true budget option that gets the job done.
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3. Fluidmaster 400CRP14 Universal Fill Valve & Flapper Kit
Who it’s for: Those with older toilets needing more than just a new fill valve.
- Key Benefits: Includes fill valve and flapper, stops multiple types of leaks.
- Pros: Great value, comprehensive repair, fits most tanks.
- Cons: Slightly more effort to install than just the valve.
Final Verdict: The smart choice if your toilet is aging and multiple parts are wearing out.
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4. Fluidmaster PRO45 Quiet Fill Valve
Who it’s for: Households that want a professional-grade, quieter toilet refill.
- Key Benefits: Noise-reducing design, durable construction, reliable sealing.
- Pros: Whisper-quiet, stronger build, longer lifespan.
- Cons: Pricier than standard valves.
Final Verdict: Best upgrade if noise and durability are top concerns.
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5. Fluidmaster 400H-002 Performax Universal Fill Valve
Who it’s for: Homeowners seeking advanced water control and efficiency.
- Key Benefits: Dual adjustments for performance and water savings.
- Pros: Saves water, customizable height, universal fit.
- Cons: Installation takes a bit longer.
Final Verdict: The best choice for eco-conscious households.
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6. Fluidmaster 402CARHRKP10 Complete Toilet Repair Kit
Who it’s for: Those who want to replace all tank components at once.
- Key Benefits: Includes fill valve, flapper, and tank-to-bowl parts.
- Pros: Comprehensive fix, long-term reliability, one kit solves multiple issues.
- Cons: More expensive and more installation work.
Final Verdict: A complete solution if your toilet has multiple leaks and worn parts.
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Comparison Table
| Name | Best For | Key Features | Price Link |
|---|---|---|---|
| Fluidmaster 400AH | All-around performance | Quiet, water-saving, adjustable | View Price |
| Fluidmaster 400A | Budget replacement | Universal, simple, proven design | View Price |
| Fluidmaster 400CRP14 | Valve + flapper repair | Complete kit, prevents leaks | View Price |
| Fluidmaster PRO45 | Quiet upgrade | Professional-grade, noise-reducing | View Price |
| Fluidmaster 400H-002 | Water efficiency | Dual adjustments, eco-friendly | View Price |
| Fluidmaster 402CARHRKP10 | Full rebuild | Complete repair kit | View Price |
FAQ Section
Why is my Fluidmaster fill valve leaking from the bottom?
Most likely because of a worn shank washer, loose or overtightened locknut, or a cracked valve body.
Can I stop the leak without replacing the valve?
Sometimes. Tightening the nut or replacing the shank washer may fix it. But if the body is cracked, you’ll need a new valve.
How long should a Fluidmaster valve last?
Generally 5–7 years, though hard water may shorten its lifespan.
Is replacing a fill valve difficult?
No. Most DIYers can do it in 20–30 minutes with basic tools.
Should I replace the whole kit or just the valve?
If your toilet is older, a full kit is a better investment. Otherwise, just swap the valve.
Conclusion
A Fluidmaster fill valve leaking from the bottom can waste water and damage your bathroom floor if left alone. While you can sometimes solve the problem by tightening or replacing the shank washer, in many cases the best long-term solution is a new valve.
For most people, the Fluidmaster 400AH is the best universal fix. If you want something affordable, go with the 400A. And if your toilet needs a bigger refresh, the 400CRP14 kit is the way to go.
Don’t put off the repair — grab the right Fluidmaster replacement today and stop that bottom leak once and for all.