Checklist • Updated Jan 12, 2026 • 12 min read

Under-sink smell checklist: P-trap, disposal, and hidden leaks

Under-sink smells usually come from moisture, food residue, or a dry P-trap. This checklist helps you narrow it down without risky DIY.

Smell types (quick identification)

Fast sniff test (where is it strongest?)

• Cabinet wood / floor: musty smell often means moisture.
• Drain area: sewer-ish smell can mean P-trap issues.
• Garbage disposal: sour/rotting smell is usually residue.

Tools & supplies

• Flashlight (leaks hide in shadows).
• Paper towels (to check “is it actively wet?”).
• Dish soap + warm water.
• Microfiber cloth (drying helps you detect return moisture).
• Trash bag (for dirty liners / food residue cleanup).

P-trap basics (why it matters)

The P-trap is designed to hold water. That water seal blocks sewer gases from entering your cabinet. If the trap dries out (rarely used sink, vacation, or a small leak), odor can rise from the drain.

Checklist

Step-by-step (low-risk)

1) Check for hidden moisture

1. Remove everything from under the sink.
2. Dry the cabinet completely (floor and walls).
3. Wrap a dry paper towel around each visible connection (P-trap joints, shutoff valves) and wait 2–3 minutes.
4. Look for damp spots. If any connection wets the towel, it’s a maintenance ticket.

1b) Overnight leak test (easy, high signal)

• Line the cabinet floor with dry paper towels (or a piece of cardboard).
• Don’t use the sink for a few hours (or overnight).
• Check in the morning: even a slow drip will show up clearly.
• If the towels/cardboard are damp, take photos and file a maintenance request.

2) Rule out a dry trap

• Run cold water for 30 seconds, then hot for 30 seconds.
• Wait 10 minutes and re-check the smell.
• If the smell returns quickly (same day), there may be a vent/seal issue: call maintenance.

2b) Where sewer smells usually come from

• Dry P-trap (most common): smell improves after running water.
• Loose connection: sewer smell + occasional dampness.
• Venting issue: gurgling sounds + sewer smell that persists.

3) Clean disposal/splash guard residue

• Safety: keep the disposal off; don’t put hands into the unit.
• Scrub the underside of the rubber splash guard with dish soap.
• Flush with hot tap water + dish soap for 60–90 seconds.

3b) Deeper disposal odor routine (still renter-safe)

• Dish soap + hot water flush first (often enough).
• Ice + salt (optional): some people use it to knock residue loose. If you’re unsure, skip it—cleaning the guard + flushing is safer and usually sufficient.
• Don’t pour grease down the drain. It coats pipes and traps food residue that smells later.

4) Check the trash/recycling zone

• Wash the bin and let it dry fully.
• Replace liners and keep the cabinet slightly cracked for airflow (if possible).

Common leak points (quick visual scan)

• Shutoff valves (small drips at the base can wet the cabinet over time).
• P-trap joints (especially after someone bumped the pipe while storing items).
• Disposal connection (where the drain line meets the disposal).
• Dishwasher hose connection (if present).

Dishwasher clue (if you have one)

If the smell appears after running the dishwasher, check under the sink afterward. A small drip from the dishwasher hose connection can create a musty cabinet quickly.

Prevention (2-minute routine)

• Keep the cabinet dry: wipe small spills immediately.
• Run the faucet weekly in rarely used sinks to keep the P-trap wet.
• Don’t store loose chemicals that can spill and create lingering odors.
• Scrape plates before using the sink/disposal—less residue, less smell.

If odors return quickly after cleaning, it’s often moisture, not “dirty dishes.” Focus on finding the source.

When to call maintenance (and what to say)

• Moisture returns after drying (hidden leak is likely).
• Persistent sewer smell even after running water.
• Any mold growth on porous cabinet material.
• Soft/swollen wood (water damage progresses fast).

Maintenance request template (copy/paste)

Subject: Under-sink odor / possible leak inspection

Hi [Landlord/Maintenance], there’s a persistent odor under the [kitchen/bathroom] sink. I checked for obvious issues and noticed [sewer smell near the P-trap / musty odor + damp cabinet / possible moisture at a connection]. Could you please inspect for a leak or vent/trap issue and repair as needed? I can share photos and I’m available [times]. Thank you.

FAQ

• Is a sewer smell dangerous? It can indicate sewer gas entering the space. If it persists after running water, report it.
• Should I pour bleach down the drain? Avoid harsh chemicals in rentals; it can damage finishes and won’t fix a trap/vent/leak issue.
• Why does it smell worse at night? Odors are more noticeable when the home is closed up and airflow is lower.

Optional: photo checklist (for your ticket)

• Wide shot under the sink (shows the layout).
• Close-up of any damp connection or stain.
• Paper towel test photo if it shows moisture.
• Timeline note: when you smell it and whether it changes after running water.

Final sanity checks

• Rarely-used sink? Run water weekly so the P-trap doesn’t dry out.
• Smell changes after running water? That points to a dry trap more than “dirty cabinet.”
• Odor + any dampness is a faster maintenance ticket than repeated cleaning.
• If you’re unsure, take photos and send a short note—catching a small leak early protects your deposit.

If you want one simple rule: smell + moisture = maintenance. Cleaning only helps if the source is residue/trash—leaks and venting issues come back.

Stop signs (call maintenance)

• Any active drip or wetness that returns after drying.
• Strong sewer smell that persists after running water.
• Visible mold growth on porous cabinet material.

Related: Slow drain guide • Monthly checklist