Sewage Smell Coming from Under the Sink
Updated February 25, 2026
Rotten or sewage odor from under the kitchen or bathroom sink -- caused by a dry P-trap, leaking drain connection, missing cleanout cap, or venting issue. This is typically a diy fix. Estimated cost: $0 - $15.
Overview
Sewer gas under the sink means the barrier between your drain system and your living space has failed somewhere. The P-trap is the primary barrier -- it holds water that blocks gas from traveling up the pipe. When the trap dries out, leaks, or is bypassed, hydrogen sulfide and methane enter the cabinet. The smell is unmistakable and can cause headaches in enclosed spaces. The fix is usually simple: run water to refill the trap, tighten a loose connection, or replace a missing cleanout cap.
Symptoms
- Rotten egg or sewage smell when you open the cabinet under the sink
- Smell is worse after the sink has not been used for several days
- Smell intensifies when the dishwasher drains or other fixtures run nearby
- Visible gap or disconnection in the drain pipes under the sink
- Water stain or dampness on the cabinet floor (indicates a slow drain leak)
Common Causes
- Dry P-trap -- the water in the trap evaporated because the sink was unused for weeks, removing the gas barrier
- Loose slip joint connection on the P-trap -- a gap in the fitting allows gas to escape even though water is present
- Missing or loose cleanout plug on the drain tee -- the small threaded plug on the side of the drain pipe
- Cracked or corroded P-trap -- old chrome traps develop pinhole cracks that leak gas before they leak water
- Improper drain connection -- the dishwasher drain hose is not looped high enough, creating a path for gas to travel back through the dishwasher connection
What You'll Need
How to Fix It
- Run Water to Refill the P-Trap
The simplest fix: run the faucet for 30 seconds. This refills the P-trap with water, restoring the gas barrier. If the smell disappears within a few minutes, the trap was dry. For seldom-used sinks, run water weekly to keep the trap full. Pour a tablespoon of mineral oil on top of the trap water to slow evaporation between uses.
Tip: Every drain in your house has a P-trap that can dry out: kitchen sink, bathroom sink, bathtub, shower, floor drains, laundry sink. If you smell sewer gas in any room, run water in every drain in that room. - Check All Drain Connections
Open the cabinet and inspect every connection: the slip joints on the P-trap, the tailpiece connection to the drain basket, the wall pipe connection, and the dishwasher drain hose connection. Tighten any loose slip nuts -- hand-tight plus a quarter turn. Check for a cleanout plug on the drain tee (a small threaded cap on the side). If it is missing or loose, gas escapes through it. Replace or tighten it. Check for cracks in the P-trap -- run your finger along the entire surface feeling for moisture.
Tip: A loose cleanout plug is one of the most common and most overlooked causes of sewer smell under a sink. It is a small fitting that many homeowners do not even know exists. Look for a threaded cap on the side of any tee or wye fitting in the drain assembly. - Check the Dishwasher Drain Hose
The dishwasher drain hose should loop up to the underside of the countertop (high loop) before connecting to the garbage disposal or drain tailpiece. This prevents drain water and gas from flowing back into the dishwasher and into the cabinet. If the hose runs straight from the dishwasher to the drain connection without a high loop, gas can travel through the hose. Zip-tie the hose to the underside of the countertop at the highest point to create the loop.
Tip: Some plumbing codes require an air gap fitting (a small device mounted on the countertop or sink) instead of a high loop. Check your local code. Either method prevents backflow and gas migration. - Replace Cracked or Corroded Drain Parts
If the P-trap is cracked, corroded chrome, or has mineral-crusted joints that will not seal, replace the entire trap assembly. A PVC P-trap kit costs $5-$10 and includes the trap, tailpiece adapter, washers, and nuts. Takes 15 minutes to swap. While you are at it, replace any corroded tailpiece sections or worn slip joint washers. Fresh connections eliminate gas leaks at every joint.
Tip: PVC drain parts are the modern standard and will not corrode. Chrome traps look nicer on exposed plumbing (pedestal sinks) but corrode internally after 10-15 years. If the trap is hidden in a cabinet, always use PVC.
When to Call a Pro
Call a plumber if the smell persists after checking all visible connections (may indicate a cracked drain pipe inside the wall), if multiple fixtures under the same sink are affected and you suspect a vent issue, or if you see sewage backing up into the cabinet (main line or branch drain blockage).
Prevention Tips
- Run water in every seldom-used sink weekly to keep the P-trap full.
- Check drain connections under every sink annually -- a 30-second visual inspection catches loose fittings before they start leaking gas.
- Replace old chrome P-traps with PVC when they start showing corrosion. A $5 PVC trap outlasts a $20 chrome trap.
- Ensure the dishwasher drain hose has a high loop or air gap to prevent gas backflow.
Frequently Asked Questions
What are the signs of a sewage smell coming from under the sink?
Rotten egg or sewage smell when you open the cabinet under the sink Smell is worse after the sink has not been used for several days Smell intensifies when the dishwasher drains or other fixtures run nearby Visible gap or disconnection in the drain pipes under the sink Water stain or dampness on the cabinet floor (indicates a slow drain leak)
What causes a sewage smell coming from under the sink?
Dry P-trap -- the water in the trap evaporated because the sink was unused for weeks, removing the gas barrier Loose slip joint connection on the P-trap -- a gap in the fitting allows gas to escape even though water is present Missing or loose cleanout plug on the drain tee -- the small threaded plug on the side of the drain pipe Cracked or corroded P-trap -- old chrome traps develop pinhole cracks that leak gas before they leak water Improper drain connection -- the dishwasher drain hose is not looped high enough, creating a path for gas to travel back through the dishwasher connection
When should I call a plumber for a sewage smell coming from under the sink?
Call a plumber if the smell persists after checking all visible connections (may indicate a cracked drain pipe inside the wall), if multiple fixtures under the same sink are affected and you suspect a vent issue, or if you see sewage backing up into the cabinet (main line or branch drain blockage).
How do I prevent a sewage smell coming from under the sink?
Run water in every seldom-used sink weekly to keep the P-trap full. Check drain connections under every sink annually -- a 30-second visual inspection catches loose fittings before they start leaking gas. Replace old chrome P-traps with PVC when they start showing corrosion. A $5 PVC trap outlasts a $20 chrome trap. Ensure the dishwasher drain hose has a high loop or air gap to prevent gas backflow.
When should I call a plumber for sewage smell coming from under the sink?
Call a plumber if the smell persists after checking all visible connections (may indicate a cracked drain pipe inside the wall), if multiple fixtures under the same sink are affected and you suspect a vent issue, or if you see sewage backing up into the cabinet (main line or branch drain blockage).
Can I fix sewage smell coming from under the sink myself?
This problem is rated "DIY". Most homeowners can handle this with basic tools and patience.
How serious is sewage smell coming from under the sink?
This is a medium-severity issue. Fix it soon to prevent it from getting worse.
How much does it cost to fix sewage smell coming from under the sink?
The estimated repair cost is $0 - $15. Costs vary by location, severity, and whether you hire a professional.
How can I prevent sewage smell coming from under the sink?
Key prevention tips: Run water in every seldom-used sink weekly to keep the P-trap full.. Check drain connections under every sink annually -- a 30-second visual inspection catches loose fittings before they start leaking gas.. Replace old chrome P-traps with PVC when they start showing corrosion. A $5 PVC trap outlasts a $20 chrome trap..