Why Is My Kitchen Sink Drain Flange Leaking? A Complete DIY Fix Guide

You pull out the cleaning supplies from under the sink and your hand lands in a damp, musty puddle. The drip is coming from right where the metal drain meets the sink basin—your flange is leaking.

A leaking drain flange is one of the most common kitchen plumbing headaches. The good news is that it’s almost always a DIY fix that takes under an hour and costs less than $15 in parts. This guide walks you through why it happens and the best way to seal it for good.

TL;DR

A leaking drain flange is usually caused by dried-out plumber’s putty, a loose locknut, or a cracked flange. The fix involves removing the old flange, cleaning the sink surface thoroughly, applying fresh plumber’s putty (or silicone for stone sinks), and reinstalling the assembly. Most repairs take 30–45 minutes and cost under $15 for a new strainer kit. If water appears only when the sink drains, the flange seal is the prime suspect.

Key Takeaways

• The seal fails over time: Plumber’s putty dries out and cracks after years of use, letting water seep between the flange and sink basin .
• Start with a simple test: Fill the sink with water and watch underneath. If drips appear at the drain connection, the flange seal is your problem .
• Material matters: Use plumber’s putty for stainless steel or porcelain sinks, but use silicone sealant for granite, marble, or composite sinks—putty can stain porous stone .
• Cleanliness is critical: Scrape away every bit of old putty before installing the new flange. Any leftover residue will prevent a proper seal .
• Don’t overtighten: The locknut should be snug, not forced. Over-tightening can crack the flange or damage the sink basin .

The Real Causes Behind a Leaking Drain Flange and How to Fix It

The drain flange, also called a basket strainer, is the metal ring visible at the bottom of your sink basin. It connects the sink to the drain pipe below and relies on a seal to keep water flowing down the pipe—not around it .

Why the Flange Leaks: Common Culprits

Dried-Out Plumber’s Putty

The most common cause is old putty that has hardened, cracked, or shrunk over time. Plumber’s putty is a clay-like compound that fills the gap between the flange and the sink. It’s waterproof but not permanent. Years of exposure to water, cleaning chemicals, and temperature changes take their toll .

A Loose or Worn Locknut

The flange is held in place from underneath by a large locknut. Vibration from daily sink use, storing heavy items that bump pipes, or just normal wear can loosen this nut. A loose nut means the flange isn’t pressed tightly against the putty, creating a gap for water to escape .

Cracked or Corroded Flange

Metal flanges can develop hairline cracks from over-tightening or rust over time. A cracked flange lets water through even if the seal is perfect. If you see rust or visible cracks around the drain, replacement is the only option .

Incorrect Sealant Type

Using the wrong sealant for your sink material can cause premature failure. For example, plumber’s putty should never be used on granite, marble, or plastic sinks—the oils can stain porous stone or damage plastic surfaces. Silicone sealant is the safer choice for these materials .

How to Fix a Leaking Drain Flange: Step-by-Step

This repair takes about 30–45 minutes and requires basic tools. Always unplug appliances before cleaning or repairing them, but for this drain repair, you don’t need to turn off the water supply since you’re only working on the drain, not the supply lines .

Tools and Materials You’ll Need:

• Replacement drain flange kit (if needed)
• Plumber’s putty or silicone sealant
• Adjustable wrench or channel-lock pliers
• Basin wrench (recommended for the locknut)
• Bucket
• Putty knife or scraper
• Clean rags

Step 1: Test to Confirm the Source

Before taking anything apart, confirm the flange is the problem. Fill the sink with a few inches of water and let it sit for a minute. Look under the sink with a flashlight. If water drips from where the drain meets the sink basin, the flange seal has failed .

Step 2: Clear Out the Cabinet and Set Up

Remove everything from under the sink. Place a bucket directly under the drain pipes to catch water when you disconnect them. Put down towels to protect the cabinet floor .

Step 3: Disconnect the Drain Pipe

Loosen the slip nut connecting the P-trap (the U-shaped pipe) to the tailpiece (the vertical pipe from the flange). Use pliers or channel-lock pliers. Most slip nuts are plastic and can be turned by hand once loosened. Let any water drain into your bucket, then carefully pull the pipes apart .

Step 4: Remove the Old Flange

From under the sink, locate the large locknut holding the flange in place. Use a basin wrench or channel-lock pliers to turn it counter-clockwise. This nut can be stubborn. If it won’t budge, apply penetrating oil and wait 10–15 minutes . Once the nut is off, push the flange up and out from the sink basin above .

Step 5: Clean the Sink Surface Thoroughly

This step is critical. Use a putty knife or scraper to remove every bit of old putty from the sink opening and the underside of the sink rim. Wipe the area clean with a rag and mild cleaner. Any leftover residue will prevent the new seal from working .

Step 6: Apply Fresh Sealant

Roll a piece of plumber’s putty between your palms into a rope about the thickness of a pencil. Press it around the underside of the new flange rim, making sure the entire circumference is covered without gaps .

If your sink is granite, marble, or composite: Use silicone sealant instead of putty. Apply a consistent bead around the underside of the flange. The oils in putty can stain these materials .

Step 7: Install the New Flange

From above, press the putty-coated flange firmly into the sink opening. Make sure it’s centered and sits flush with the basin surface .

Step 8: Tighten from Below

Under the sink, slide the rubber gasket and friction ring onto the threaded body of the flange, then thread on the locknut. Tighten by hand first, then use a basin wrench to snug it. Tighten until you see excess putty squeeze out evenly around the flange rim—this is the “squish test” that confirms a good seal. Do not overtighten—you can crack the flange or the sink .

Step 9: Reconnect and Test

Reattach the tailpiece and P-trap, tightening the slip nuts securely. Run water into the sink and check underneath for leaks. If all is dry, you’ve fixed it. Wipe away any excess putty that squeezed out .

Simple Tips to Prevent Future Leaks

• Inspect under the sink every few months: A quick visual check can catch a loose nut or failing seal early.
• Use silicone on stone sinks: If you have a granite or marble sink, always use silicone sealant, not putty .
• Don’t store heavy items near pipes: Bumping the drain assembly can loosen connections over time .
• Replace the flange if it’s over 10 years old: Even if it’s not leaking, aging metal can develop hidden cracks.

When to Call a Professional Plumber

This repair is DIY-friendly, but call a plumber if:

• The flange is stuck and you can’t loosen the locknut even with penetrating oil.
• The sink basin is cracked: This requires professional replacement.
• Water is coming from inside the wall: That’s a different problem that needs expert attention.

“A leaking drain flange is one of the easiest kitchen plumbing fixes. The secret is thorough cleaning before you apply new sealant—any old putty left behind will cause the new seal to fail.”

Frequently Asked Questions (FAQs)

1. Why is my kitchen sink drain flange leaking even after I tightened it?
Tightening won’t fix a dried-out putty seal or a cracked flange. You need to remove the flange, clean the surface, and apply fresh putty or silicone .

2. Can I use plumber’s putty on a granite sink?
No. Plumber’s putty contains oils that can stain granite, marble, and other porous stone. Use silicone sealant instead .

3. How long does plumber’s putty last?
It typically lasts 5–10 years, depending on water quality and exposure to cleaning chemicals. When it hardens or cracks, it needs replacement .

4. What’s the difference between a drain flange and a basket strainer?
They’re the same thing. “Drain flange” is the technical term for the metal ring in the sink bottom. “Basket strainer” refers to the same part with the strainer screen inside .

5. How do I know if the flange is cracked or just the seal is bad?
Inspect the flange carefully after removal. If you see hairline cracks, rust, or corrosion, replace it. If it looks solid, fresh putty usually fixes the leak .

6. Do I need to turn off the water to replace the drain flange?
No. The drain flange is on the drainage side, not the water supply side. You can leave the water on, though it’s not needed during the repair .

References

Trusted Sources for Kitchen Sink Drain Repairs:

• Loctite – How to Seal a Kitchen Sink Drain
• Las Vegas Review-Journal – Likely Causes for Leak Under Sink
• Engineer Fix – How to Change a Kitchen Sink Drain
• Fix Up First – Broken Kitchen Drain Basket Guide

Which kitchen problem do you want solved next? Share your thoughts in the comments.