Why Your Kitchen Sink Strainer Keeps Leaking (Even After You’ve Replaced It)
You’ve done this before. The old strainer was crusty, stained, and dripping, so you pulled it, bought a new basket strainer kit, and put it back together following the instructions on the box. A few days later, that same wet ring shows up under the sink again.
If you’ve already replaced a leaking kitchen sink basket strainer once or twice and it’s still not sealing, the part probably isn’t the problem. Four assembly details cause most repeat leaks, and all four are fixable without buying a third kit.
It’s Rarely the Strainer Kit’s Fault
Basket strainer kits are simple, standardized hardware: a flange, a gasket, a locknut, and a tailpiece connection. When a new kit leaks the same way the old one did, the cause is almost always how it was seated and tightened, not the part itself. Here’s where that usually goes wrong.
Failure Point 1: The Locknut Is Over-Tightened or Under-Tightened
It feels intuitive to crank the locknut down as hard as it’ll go to “make sure it’s sealed.” That’s usually what causes the leak. Overtightening crushes the putty or gasket instead of letting it form an even seal, and it can warp thin sink metal enough to open a gap on one side. Undertightening does the opposite, leaving the flange loose enough that water works its way underneath. The target is snug and even, just hand-tightened plus a slight turn with channel locks, avoiding maximum torque.
Failure Point 2: Plumber’s Putty That Dried Out or Wasn’t Seated Right
Plumber’s putty vs. silicone gets treated like a rivalry, but putty isn’t the outdated choice people assume it is. It stays pliable indefinitely if it’s stored sealed and applied correctly. Most putty leaks come down to a dried-out, crumbly ball that was left uncovered in the toolbox, or putty that wasn’t rolled into a complete, even rope before it was pressed down, leaving gaps instead of a continuous seal. Oatey’s application guidance is a useful reference for getting this step right.
That said, putty isn’t right for every application. It can degrade certain plastic strainer bodies (ABS or acrylic) over time and will stain porous stone sinks. In those cases, 100% silicone sealant is the better call. The honest answer to “putty or silicone” is: check what your strainer body and sink are made of, then pick accordingly.
Failure Point 3: A Cracked Slip Nut from Over-Torquing
The slip nuts connecting the strainer’s tailpiece to the trap are almost always plastic. They only need to be hand-tight plus a quarter turn with pliers. Wrenching them down hard enough to “guarantee” a seal is a common way to hairline-crack the nut or crush the washer inside it unevenly. That kind of crack doesn’t always leak right away. It can weep for weeks before it’s noticeable, which is why a second “fix” may not hold.
Failure Point 4: Reusing the Old Tailpiece with a New Strainer
Reconnecting a new basket strainer to the old tailpiece and washers is a common shortcut, and a frequent source of leaks that show up after the repair. Old gaskets lose compression over time, tailpiece threads can be slightly worn or corroded, and thread pitch isn’t always identical across brands. A new strainer paired with old, fatigued parts often looks like a proper fit while sealing poorly.
How to Do the Swap Right, Step by Step
- Remove the old strainer. Loosen the slip nut, then the locknut under the sink, using pliers or a basket strainer wrench. A few taps with a rubber mallet can free a seized one.
- Clean the sink opening down to bare metal. Old putty, grease, and grime will keep a new seal from forming.
- Choose your sealant by material. Roll putty into an even, foot-long rope for a metal strainer body, or use 100% silicone for a plastic body or stone sink.
- Seat the new strainer, holding it from above while you work underneath.
- Hand-tighten the locknut, then snug it with channel locks until a thin bead of putty oozes out, but not so tight that you strain the fitting.
- Reconnect the tailpiece with new washers, not the old ones, and hand-tighten the slip nuts before a quarter turn with pliers.
- Wipe away excess putty, run water for a few minutes, and check every connection underneath.
- Recheck it after 24 hours. Some slow leaks only appear once the fitting has settled under normal use.
This Old House’s strainer replacement walkthrough is a solid visual reference if you want to see these steps in sequence.