How to Install a Kitchen Sink Basket Strainer (Leak-Free)

A slow drip under the kitchen sink often traces back to the basket strainer, not the pipes. Over time the putty dries out, the rubber gasket hardens, and the big locknut loosens just enough to let water seep past the flange every time the sink fills. Knowing how to install a sink strainer properly lets you fix that drip in about an hour with a few basic tools, and a quality stainless strainer body will outlast several cheaper replacements.

The job has three parts: removing the old strainer (which is often the hardest step because the locknut seizes), sealing the new flange to the sink with plumber’s putty or a rubber gasket, and tightening everything evenly so it seals without cracking the sink or deforming the gasket. Installing sink strainer hardware for the first time and replacing a sink basket that has started to leak follow the same steps, covered here for a standard kitchen sink basket strainer in a sink without a garbage disposal. Disposals use a different mounting flange and are a separate job.

How to Install a Sink Strainer: Tools and Materials

• New kitchen sink basket strainer assembly (flange, rubber gasket, friction washer, locknut, tailpiece coupling)
• Plumber’s putty, or a strainer designed to seal with its rubber gasket alone
• Groove-joint pliers, 10 to 12 inch
• Spud wrench or sink strainer wrench (for the large locknut)
• Strainer removal tool or two long-nose pliers (to hold the flange from above)
• Flat screwdriver and a hammer, or a hacksaw blade, for a seized nut
• Bucket, towels and a flashlight
• Plastic putty knife, mineral spirits and a scouring pad for cleanup
• Safety glasses and gloves

Before buying, check that the new strainer matches your sink opening (nearly all kitchen sinks use a 3.5-inch opening) and that the tailpiece connection matches your existing drain, typically 1.5-inch.

Step 1: Prepare the Work Area

Empty the cabinet, lay a towel down, and place a bucket under the drain. You do not normally need to shut off the water supply for a strainer swap, since you are working on the drain side, but turn the faucet off firmly and make sure no one runs water while the drain is open. If the dishwasher drains into this sink, do not run it until you finish.

Loosen the slip nut that connects the strainer tailpiece to the drain pipe or trap. It usually turns by hand; use groove-joint pliers if it is stiff. Let the trapped water drain into the bucket, then pull the tailpiece free.

Step 2: Remove the Old Strainer and a Seized Locknut

The large locknut under the sink holds the strainer body tight against the sink. Fit a spud wrench or strainer wrench to its lugs and turn counterclockwise, looking up from below. Have a helper hold the flange from above with a strainer removal tool or with the handles of two pliers crossed in the crossbars so the whole body does not spin.

Old locknuts are often corroded in place. Try these in order:

1. Spray penetrating oil on the threads and wait 15 minutes.
2. Place the tip of a flat screwdriver against one lug of the nut and tap it counterclockwise with a hammer. Short, firm taps break corrosion better than steady pressure.
3. If the nut still will not turn, cut it. Use a hacksaw blade held in a rag or a mini hacksaw to slice through one side of the nut, angled so you do not cut the sink. Then pry the nut open with the screwdriver.

With the nut off, push the strainer body up and out of the sink. Scrape away all old putty from the sink opening with a plastic putty knife, then clean the area with mineral spirits and a scouring pad. Any leftover putty or grit can cause a new leak.

Step 3: Choose Putty or a Rubber Gasket

This is the step that decides whether the new strainer leaks. There are two ways to seal the flange to the top of the sink.

Plumber’s Putty

Roll a rope of putty about 3/8 inch thick and press it evenly around the underside of the strainer flange. Putty works on stainless steel, enameled cast iron and most fireclay sinks, and it fills small irregularities in the sink surface. Use a stain-free putty on natural stone or composite sinks, since standard putty can leave oily marks on porous surfaces. Many manufacturers of composite sinks recommend silicone or a rubber gasket instead, so check the sink’s care guide.

Rubber Gasket Only

Many newer strainers include a thick rubber gasket designed to seal between the flange and the top of the sink without putty. This is cleaner and works well on flat, smooth sink openings. On a sink with a slightly curved or textured opening, a gasket may not seal fully; in that case putty is the safer bet.

Do not use both putty and a top gasket together unless the strainer instructions say to. Stacking them can prevent the flange from seating flat.

Step 4: Install the New Strainer

1. Press the flange, with putty or its top gasket, down into the sink opening. Push firmly and evenly so the seal squeezes out slightly all the way around.
2. From underneath, slide on the thick rubber gasket first, then the friction washer (usually a fiber or paper ring). The friction washer lets the locknut turn without twisting the rubber gasket.
3. Thread on the locknut by hand until snug. Keep the flange from turning with the removal tool or pliers from above.
4. Tighten the locknut with the spud wrench, alternating small turns and checking that the flange stays centered. Stop when putty stops squeezing out and the nut is firm. On a fireclay or cast iron sink, avoid heavy force, which can crack the sink around the opening.
5. Wipe away the excess putty from the top of the sink with a finger and a rag.
6. Attach the tailpiece to the strainer body with its coupling nut and washer, then reconnect the tailpiece to the drain with its slip nut and washer. Hand-tighten, then give each nut a quarter turn with pliers.

If the tailpiece does not line up with the drain, you may need a slightly shorter or longer tailpiece. Do not force misaligned pipes together, because the stress will cause a leak later.

Step 5: Leak Test

The final part of learning how to install a sink strainer is testing it. A proper leak check fills the sink, not just runs water through it. Put the basket in the closed position and fill the sink to about 2 inches below the rim. Let it sit for 10 minutes while you look under the sink with a flashlight and run a dry paper towel around the flange, locknut and slip joints. Then pull the basket and let the full sink drain all at once, which pressurizes the tailpiece and trap joints, and check again.

If you see moisture at the flange, tighten the locknut another small amount. If the leak continues, remove the strainer and reseat it with fresh putty. Drips at the tailpiece or trap usually mean a washer is misaligned or a slip nut needs a little more tightening.

Troubleshooting Common Strainer Problems

The strainer spins when tightening. You need someone or a tool holding the flange from above. A basket strainer removal tool that wedges in the crossbars is inexpensive and makes the job much easier.

Leak returns after a few weeks. The locknut may have loosened as the putty settled. Snug it up a quarter turn. If the rubber gasket is thin or cracked, replace it.

The basket will not seal and water drains slowly away. The stopper gasket on the basket is worn. Replacement baskets are sold separately and usually fit standard strainer bodies.

Water drips from inside the cabinet but not at the strainer. Check the dishwasher drain hose, the faucet supply lines and the trap. Those leaks are sometimes mistaken for strainer leaks.

Cost Ranges

A basic kitchen sink basket strainer usually costs about $10 to $25, while heavier stainless models with better baskets run roughly $25 to $60. A spud wrench or strainer wrench adds about $10 to $25, and plumber’s putty costs a few dollars. If you hire the job out, most plumbers charge in the range of $125 to $300 for a strainer replacement, depending on local rates and whether the old nut has to be cut.

When to Call a Licensed Professional

Replacing a basket strainer is a beginner-friendly repair, but bring in a licensed plumber if the drain pipes themselves are corroded, cracked or made of old galvanized steel, if the trap arm is loose in the wall, or if the sink has an unusual or undersized opening. Adding a garbage disposal, rerouting the drain, changing vents or connecting a new dishwasher drain are plumbing changes that may require a permit and should follow local plumbing code, so a licensed plumber is the right call. Disposals also involve electrical work: any new outlet or hardwired connection under the sink should be installed by a licensed electrician, protected by a GFCI, and before touching any existing wiring, turn off the breaker and confirm the power is off with a non-contact voltage tester. If water has soaked the cabinet floor for a long time and you see mold larger than about 10 square feet, have it professionally assessed.