Leaks only while the sink is draining
The cabinet stays dry until you run water, then you see drips at the drain assembly or trap.
Start here: Start with the basket strainer, tailpiece joints, and P-trap connections.
Kitchen sink leak guide
Kitchen Sink Drain Leaking
Direct answer: A kitchen sink drain usually leaks from the first joint above the drip you see: the basket strainer under the sink, the tailpiece connection, or a loose or cracked P-trap slip joint. Figure out whether it leaks only while draining or all the time before you touch parts.
Most likely: Most often, the leak is a loose slip-joint nut, a crooked washer, or a basket strainer that has lost its seal to the sink bowl.
Put a dry towel under the drain, empty the cabinet, and run a short test while watching with a flashlight. Reality check: water often travels along pipes and drips from the lowest point, so the drip is not always the leak. Common wrong move: tightening every nut hard with pliers can crack plastic trap parts or distort washers.
Don’t start with: Don’t start by replacing the whole faucet or smearing sealant around every joint. That usually hides the source and makes the real repair messier.
Leaks only when water runs outFocus on the basket strainer, tailpiece, trap joints, and any branch connection from the sink drain.
Leaks even when the sink is idleLook higher first for faucet hoses, shutoff valves, or supply lines wetting the drain area before you chase the drain.
Last reviewed: 2026-04-04
Start by matching when and where the leak shows up
Drip forms right under the sink bowl
Water shows up around the large drain fitting directly below the sink basin.
Start here: Check the kitchen sink basket strainer seal before the lower trap parts.
Leak is lower near the curved trap
The drip hangs from a slip nut, trap bend, or trap arm connection.
Start here: Check for a loose nut, misaligned washer, or cracked kitchen sink P-trap piece.
Cabinet is wet but you cannot catch the leak in the drain test
The drain looks dry during a short run, but the cabinet floor or back wall gets wet later.
Start here: Dry everything completely and rule out faucet supply leaks, sink rim splashes, or a dishwasher branch leak before replacing drain parts.
Most likely causes
1. Loose or misaligned kitchen sink P-trap slip-joint connection
This is the most common drain-side leak, especially after the trap was bumped while storing items or after a clog was cleared.
Quick check: Dry the nut and joint, run water for 30 seconds, and watch for a bead forming right at the slip nut.
2. Kitchen sink basket strainer seal leaking at the sink bowl
If water appears high under the sink directly below the drain opening, the strainer seal is a stronger suspect than the trap.
Quick check: Fill the basin with a few inches of water, then release it and watch the underside of the strainer body as the water rushes out.
3. Cracked kitchen sink tailpiece or P-trap part
Hairline cracks drip only under flow and can look like a loose joint until you dry the pipe and inspect closely.
Quick check: Wipe the pipe dry and look for a fine split, especially near threaded areas and slip nuts.
4. Water from above is tracking down onto the drain
A faucet hose, shutoff valve, sink rim splash, or dishwasher branch can wet the drain assembly and make the drain look guilty.
Quick check: Dry everything, then test the faucet and supply area first without filling the sink, followed by a separate drain-only test.
Step-by-step fix
Step 1: Trace the first wet point before you tighten anything
You want the highest point where fresh water appears. That tells you whether this is really a drain leak or water running down from somewhere else.
- Empty the cabinet so you can see the full drain and supply area.
- Place a dry towel or shallow pan under the sink.
- Use a flashlight and dry the basket strainer, tailpiece, trap, supply lines, shutoff valves, and cabinet floor.
- Run the faucet briefly without filling the sink and watch for drips from supply lines or faucet hoses.
- Then stop the faucet, dry again, fill the sink partway, and drain it while watching the drain assembly from top to bottom.
Next move: If you catch the first wet point, you can stay focused on that exact connection instead of guessing. If everything looks dry during both tests but the cabinet still gets wet later, check for splash at the sink rim, a dishwasher branch leak, or moisture from another nearby line.
What to conclude: A leak that appears only during draining is usually in the kitchen sink drain assembly. A leak that appears with the faucet running but before draining is often a supply-side issue.
Stop if:
- Water is pouring fast enough to damage the cabinet or floor.
- You cannot safely reach the area without forcing pipes or electrical cords.
- The leak appears to be inside the wall or behind the cabinet back.
Step 2: Snug the slip-joint nuts and straighten the trap assembly
A slightly loose or crooked slip-joint connection is the most common easy fix, and it is safer than tearing the drain apart right away.
- Start at the leaking slip-joint nut only, not every fitting under the sink.
- Hand-tighten the nut first. If needed, give it a small additional turn with pliers while supporting the opposite side so the pipe does not twist.
- Check whether the trap and tailpiece are lined up naturally. If the pipes are under side-load, loosen the joint slightly, straighten the assembly, and retighten.
- Run water again and watch the same joint.
Next move: If the drip stops and the joint stays dry through a full drain cycle, the washer was likely just loose or slightly out of line. If the joint still beads water, the washer may be crooked, worn, or the pipe may be cracked.
What to conclude: A joint that seals after a light adjustment usually did not need new parts. A joint that keeps leaking after proper alignment usually needs to come apart for inspection.
Step 3: Take apart the leaking joint and inspect the washer and pipe
Once a specific joint is confirmed, opening just that connection tells you whether you have a simple washer issue or a damaged drain piece.
- Put a bucket under the trap and loosen only the leaking joint.
- Slide the nut back and inspect the kitchen sink slip-joint washer for flattening, splits, or a crooked seat.
- Check the mating pipe for cracks, out-of-round ends, or damaged threads near the nut.
- Reassemble carefully with the washer facing the correct direction for the joint, then hand-tighten and snug lightly.
- Test with a full sink drain, not just a quick trickle.
Next move: If the joint stays dry after reassembly, the washer was likely misseated or the joint was assembled crooked. If the washer is damaged or the pipe is cracked, replace the exact leaking kitchen sink drain piece instead of overtightening it.
Step 4: Check the kitchen sink basket strainer if the leak starts high under the bowl
When water appears around the large drain fitting under the sink, the basket strainer seal is a stronger suspect than the trap below it.
- Dry the underside of the sink around the basket strainer completely.
- Fill the sink with a few inches of water, then release it while watching the strainer body and locknut area.
- If water forms around the strainer body before the tailpiece gets wet, try snugging the basket strainer mounting hardware evenly just enough to seat it better.
- Retest. If it still leaks from the strainer-to-sink connection, plan on removing and resealing or replacing the kitchen sink basket strainer.
Next move: If a light, even snug stops the seep, the strainer had loosened slightly and the seal re-seated. If the leak returns from the same high point, the basket strainer seal has likely failed and needs to be rebuilt or replaced.
Step 5: Replace only the failed drain part and retest with a real load of water
By now you should know whether the fix is a washer-level repair, a cracked trap or tailpiece, or a basket strainer replacement. Finish with a full test so you do not leave a slow leak behind.
- Replace the confirmed failed part: the kitchen sink basket strainer, kitchen sink P-trap, or kitchen sink tailpiece, depending on where the leak started.
- Reassemble the drain so the pipes meet naturally without being forced sideways.
- Tighten slip-joint connections firmly but not aggressively.
- Run the faucet, then drain a full basin while watching every repaired joint with a dry paper towel.
- Check again 10 minutes later for a slow forming drip on the underside of each connection.
A good result: If all joints stay dry through a full drain and follow-up check, the repair is done.
If not: If the repaired area stays dry but the cabinet still gets wet, the source is likely outside the drain path and you should inspect the faucet supply side, sink rim, or dishwasher branch next.
What to conclude: A dry full-load test confirms the leak source was correctly identified. If water still appears elsewhere, you were dealing with more than one leak path.
Replacement Parts
Kitchen sink slip joint washer set
Kitchen sink P trap kit
Kitchen sink tailpiece
Kitchen sink basket strainer
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FAQ
Why does my kitchen sink leak only when I drain water?
That usually points to the drain side, not the supply side. The most common spots are the basket strainer under the sink bowl, the tailpiece joint, or a P-trap slip joint that is loose, crooked, or cracked.
Can I just tighten every nut under the sink?
No. Start with the exact joint that gets wet first. Overtightening every connection can crack plastic trap parts, distort washers, and create a bigger leak than you started with.
How do I tell if the basket strainer is leaking instead of the P-trap?
Dry everything, then watch the underside of the sink while a full basin drains. If water appears around the large drain body directly under the sink before the lower pipes get wet, the basket strainer seal is the better suspect.
Do I need plumber's putty or sealant for a leaking slip-joint nut?
Not for a normal slip-joint repair. Those joints seal with the washer and proper alignment. If the joint leaks, inspect the washer and pipe condition instead of smearing sealant on the outside.
What if the drain parts stay dry but the cabinet floor still gets wet?
Then the drain may not be the source. Check faucet hoses, shutoff valves, sink rim splash, the base of the faucet, and any dishwasher branch connection. Water often runs along pipes and fools you into blaming the drain.
Should I replace the whole kitchen sink drain assembly at once?
Only if several parts are leaking, badly corroded, or poorly fitted together. If one washer, one tailpiece, or one basket strainer is clearly the problem, replacing just that failed part is usually the cleaner repair.