Replace a Leaking Kitchen Sink Strainer

Leaking kitchen sink strainers are one of those small failures that snowball into water damage if you ignore them. The strainer is the basket that sits in your drain opening—it catches food waste while letting water through. When the seal fails, water pools under your sink, darkens your cabinet floor, and eventually rots the wood. The good news: this is a straightforward repair that requires no special skills, just basic hand tools and patience working upside down under the sink. Done right, your new strainer will seal tight and handle another decade of daily use.

1. Kill the Water First. Locate the shutoff valves under the sink—one for hot, one for cold. Turn both valves clockwise until they stop. Run the faucet to confirm water is off. Fill the sink bowl halfway and let it drain completely, or use a cup to remove any standing water.
2. Document Before You Disconnect. Place a bucket under the curved P-trap pipe (the U-shaped section below the drain). Use two wrenches—one to hold the fitting stationary, one to loosen the locknut connecting the P-trap to the tailpiece. Turn counterclockwise. When loose enough, unscrew by hand. Water will drain into the bucket. Set the P-trap aside.
3. Find the Hidden Locknut. Get under the sink with a headlamp or flashlight. Look up at the bottom of the sink opening. You'll see the tailpiece (the vertical pipe extending down from the sink hole) and the locknut ring holding it in place. This nut is what secures the entire strainer assembly.
4. Unbolt the Old Assembly. If the nut has ears (protrusions), use a strainer locknut wrench or large pliers to grip and turn counterclockwise. If it's a slotted nut, a large flathead screwdriver and hammer work—tap the screwdriver counterclockwise. If it's ribbed plastic, try hand-turning first; if stuck, wrap it with a rubber band for grip and use pliers. Work steadily; forcing it risks cracking the sink. Once loose, unscrew by hand and remove the rubber gasket underneath.
5. Clear the Crud Away. With the old strainer out, you'll see the underside of the sink. Scrape away old plumber's putty and mineral deposits using a putty knife or old plastic scraper. Wipe with a damp cloth and let dry completely. Check for cracks or damage to the sink material around the opening. If you see cracks, the sink needs replacement—stop here and plan for that.
6. Rope the Seal Tight. Take the new strainer out of its box. Roll plumber's putty between your palms into a rope about the thickness of a pencil and roughly 36 inches long. Press this rope around the underside lip of the strainer basket—the flat ring where it meets the sink. Work it smooth and even. The putty creates a watertight seal when the strainer is pressed down.
7. Set It Level and True. From above the sink, carefully lower the strainer basket into the drain hole, making sure the putty rope stays in place around its underside edge. Center it so it sits flat and level. Press down firmly—you should feel the putty compress and seal against the sink. The strainer should not wiggle.
8. Snug the Locknut Down. Slide the rubber gasket up the tailpiece from underneath. Screw the locknut onto the threads by hand first, then tighten with your tool. For a metal strainer nut with ears, use the strainer wrench; for slotted nuts, use the screwdriver and gentle hammer taps. Tighten firmly but not aggressively—you're looking for a solid seal, not a white-knuckle grip. The strainer should not spin or shift when you wiggle it from above.
9. Clean Up Excess Putty. Look into the sink from above. Squeeze out any excess putty that oozed up around the strainer flange. Use your finger or a putty knife to clean the edges. The putty around the perimeter should be barely visible—just enough to see that a seal is there. Wipe the sink bowl clean with a damp cloth.
10. Reconnect the Trap Line. Slide the P-trap back into position. Hand-screw the locknut connecting it to the tailpiece, then use two wrenches to tighten—one holding the fitting, one turning the nut clockwise. Tighten snugly but again, not aggressively. The P-trap should sit aligned with the wall and the tailpiece, with no gaps at the threads.
11. Watch for the Leak. Turn both shutoff valves counterclockwise to restore water pressure. Run hot and cold water at the sink for 30 seconds. Watch from underneath with your flashlight for any drips at the strainer locknut or P-trap connections. Fill the sink bowl completely and let it drain—watch again. If water pools under the sink, you have a leak.
12. Diagnose and Fix Leaks. If water drips at the locknut, the gasket or seal is incomplete. Turn off water, unbolt the locknut, and check the gasket for cracks or improper seating. If damaged, replace it. If intact, recheck the putty seal around the strainer flange from above—you may need to pull the strainer and reapply putty. If water leaks at the P-trap connection, tighten that locknut one more quarter-turn. Never over-tighten the strainer nut itself—over-tightening compresses the gasket and causes failure.