Replace the basket strainer when the first drop appears where its body meets the underside of the sink, or when the flange is loose, pitted, or rusted through. Dry the whole drain and test before buying anything. A drip at the tailpiece nut, P-trap, faucet, or disposal needs a different repair.
The seal has to work in two places: the top flange must bed evenly against the sink, and the gasket stack below must clamp without twisting. Keep the old pieces in order, match the new kit before applying sealant, and do not try to cure a crooked flange by tightening harder.
Before you start: Put a shallow pan and towels under the drain, then photograph the old strainer, gasket stack, and tailpiece connection. Check the sink material and the instructions for both the sink and replacement strainer before choosing plumber's putty or silicone. Regular putty can stain porous surfaces, and it is not compatible with every plastic part.
Dry the flange, strainer body, tailpiece nut, trap, disposal connection, and supply lines. Test while the sink holds water. Test again as it drains. The first drop separates a flange leak from a lower drain leak.
Look for: A bead forms where the threaded strainer body passes through the sink. The top flange may also shift, spin, pit, or show failed sealant.
Choose another repair if: A basket-strainer replacement fits this symptom. Inspect the opening after removal. The new flange still needs a flat, sound surface.
Look for: The flange stays dry. Water appears at the tailpiece coupling, a slip-joint washer, the P-trap, or a branch connection only as the sink drains.
Choose another repair if: Repair that lower joint instead. A new basket strainer will not seal a crooked tailpiece or a worn trap washer.
Look for: A disposal hangs from the flange. The old drain may instead have a proprietary shape, overflow path, unusual outlet, or gasket-only design.
Choose another repair if: Use the manufacturer's matched parts and instructions. Do not substitute a standard basket strainer because the opening looks close.
Hold water in the sink before you release it. Watch the strainer joint first. If it becomes wet while the lower drain stays dry, the flange or gasket stack is leaking. Lay out every new piece before it disappears under the sink.
Use it for: To steady the tailpiece and loosen slip nuts without twisting the rest of the drain out of alignment.
Shop channel-lock pliers
Use it for: To engage a lugged strainer locknut where ordinary pliers cannot grip squarely in the tight cabinet space.
Shop basket strainer tools
Use it for: To lift old putty and residue without gouging the sink surface around the drain opening.
Shop putty knives
Use it for: To catch the water left in the tailpiece and trap when the drain connection comes apart.
Shop drain catch pans
Use it for: To dry each joint and make the first fresh drop easy to see during diagnosis and final testing.
Shop shop towels
Use it for: Use it when the sink and strainer instructions both approve putty. Skip it when either one calls for silicone.
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If it works: The first fresh drop forms at the basket-strainer-to-sink joint, or the flange is visibly loose, pitted, or rusted through.
If it doesn’t: If the strainer stays dry, follow the first wet joint. Tighten or rebuild the leaking tailpiece or slip joint, or trace a faucet, supply-line, disposal, or dishwasher-hose leak instead.
If it works: The replacement fits the opening and tailpiece, its parts are complete, and you know which sealing material and gasket order its manufacturer specifies.
If it doesn’t: Return or exchange the kit before opening sealant. A close-looking flange does not make up for the wrong body length, outlet, stopper style, or gasket stack.
If it works: The tailpiece is clear of the strainer, the drain remains supported and aligned, and the lower fittings are reusable or have matching replacements ready.
If it doesn’t: If the tailpiece cannot move straight down, loosen the next slip joint and realign the pieces gently. Do not lever the pipe sideways against the wall connection.
If it works: The old assembly is out and both faces of a sound sink opening are clean, smooth, and dry.
If it doesn’t: If the locknut will not turn with a strainer wrench, do not reach for a cutting wheel in a crowded cabinet. It can nick the sink, tailpiece, supply hoses, or disposal wiring. Call a plumber if you cannot shield those parts and control the tool.
If it works: The flange sits flat and centered, the gasket and friction washer are not folded or squeezed out, and the body does not spin under light hand pressure.
If it doesn’t: If the flange tips, spins, or squeezes material out on only one side, take it back apart. Clean off the used bedding material and reset it with fresh material rather than tightening a crooked assembly.
If it works: The flange stays dry while the sink holds water, every lower joint stays dry while it drains, and the strainer remains flat and still.
If it doesn’t: Trace the first wet point. A flange leak needs a clean reset. A tailpiece or trap leak needs the correct washer, straight alignment, and snug coupling nut.
Buy only after you compare the opening, flange, threaded body length, sink thickness, outlet, basket style, gasket stack, and approved sealant with the old installation.
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Check both product instructions. Regular putty suits many metal strainers in stainless steel. Granite, marble, quartz, ABS, and acrylic may require stain-free putty or silicone.
On a common metal assembly, press the rubber gasket flat against the underside of the sink. Set the thin fiber washer below the rubber, then install the locknut. The fiber layer lets the nut turn without dragging the gasket. If the parts diagram shows a different order, use that order.
Dry the drain and find the first drop. Water at the underside of the flange usually means the opening was not fully clean and dry, the flange tilted, the sealant was wrong or uneven, or the gasket twisted. Water lower down points to the tailpiece washer, alignment, or another slip joint.
Compare the old and new flange width, threaded body diameter and length, sink thickness allowance, outlet and tailpiece connection, basket or stopper style, gasket stack, and locknut. Do not rely on the top flange diameter alone.
Use the new gasket and washers supplied for the replacement. Apply fresh compatible putty or sealant whenever the flange is removed or reset; old bedding material may be contaminated, flattened, or unable to form a continuous seal.
Not always. If the tailpiece can drop straight down after its coupling nut is removed, the trap may stay in place. Loosen or remove more of the drain only when you need clearance, and support the wall arm so the extra movement does not open another leak.
Basket-strainer designs vary. The parts sheet controls the gasket order, bedding material, and tightening method. The sources below show a common metal assembly and explain when putty belongs under the flange. If the sink or strainer instructions call for silicone, use silicone instead.