Persistent drain odors are more than a nuisance—they’re a clue that something isn’t right with water seals, venting, or organic buildup in your plumbing.
The good news: most smells can be solved with a few targeted steps. Below is a practical, step-by-step guide our Long Beach Plumbing experts recommend, created by A1 Best Plumbing, to banish musty or sewer-like odors and keep them from coming back.
Quick Answer (What to Try First)
- If it smells like rotten eggs/sewer: Fill the P-trap with water, fix a dry or siphoning trap, and ensure the vent is clear.
- If it smells musty or stale: Remove biofilm from stoppers, overflows, and drain walls; use an enzyme cleaner.
- Garbage disposal smells: Clean the splash guard, grind ice/salt, and deodorize with citrus.
- Laundry drain smells: Sanitize the washer and standpipe, and confirm proper trap/standpipe height.
Our Long Beach Plumbing experts recommend addressing the source (trap, vent, or biofilm) before masking the odor with fragrances.
Why Drains Smell: The Three Usual Suspects
- Dry or compromised P-trap (sewer gas)
- Every fixture has a P-trap that holds water to block sewer gas. If it evaporates (infrequent use), leaks, or gets siphoned, odors rise.
- Clues: intense sulfur/sewer smell, especially after a flush elsewhere or when HVAC runs; gurgling.
- Biofilm buildup (musty/mildew)
- Soap scum, toothpaste, hair, food grease, and lint create a breeding ground for bacteria that smell earthy or stale.
- Clues: smell strongest right at the drain opening or overflow; improves with cleaning but returns if habits don’t change.
- Venting or sewer issues
- Blocked roof vents, failed air admittance valves (AAVs), partial mainline clogs, or a missing/loose cleanout cap can pull traps dry or push odors back into the home.
- Clues: multiple fixtures gurgle or smell, odors worsen in windy weather, slow drains across the house.
Our Long Beach Plumbing experts recommend diagnosing in that order: trap seal, biofilm, then venting/mainline.
Sink Odors: Step-by-Step Fix
- Restore/verify the trap seal
- Run water for 30–60 seconds to refill the P-trap.
- Check under-sink for dampness, corrosion, or a loose slip nut. Tighten by hand plus a quarter turn.
- Deep-clean the drain, stopper, and overflow
- Remove the pop-up stopper; scrub off gunk with a brush and dish soap.
- Feed a small bottle brush into the overflow channel (bathroom sinks) with a 1:1 mix of hot water and vinegar.
- Flush with kettle-hot (not boiling) water if you have PVC. Avoid boiling water on porcelain sinks and PVC traps.
- Biofilm treatment
- Apply an enzyme-based drain cleaner overnight per label. These digest organics without damaging pipes.
- Optional deodorizer: sprinkle 1/2 cup baking soda followed by 1/2 cup warm vinegar; after foaming stops, rinse with hot water. This freshens odors but won’t clear clogs.
- Garbage disposal care (kitchen)
- Unplug or switch power off. Clean the underside of the black rubber splash guard—it harbors odor-causing sludge.
- Restore power. Grind a tray of ice with a handful of rock salt to scour the chamber; finish with citrus peels for scent.
- Our Long Beach Plumbing experts recommend a monthly enzyme dose to keep disposal biofilm at bay.
- If odors persist
- Inspect for a dishwasher knockout plug left in the disposal (can trap food water) or a failed AAV under the sink.
- Consider replacing old corrugated dishwasher hoses with smooth-wall hoses to reduce debris retention.
Shower/Tub Drain Odors: What Works
- Hair and soap removal
- Lift the strainer; remove hair mats. A plastic barbed “zip” tool helps.
- Flush with hot water and enzyme cleaner to dissolve biofilm further into the trap arm.
- Trap and weep holes
- If you have a tile shower with a clamping drain, clogged weep holes can trap stagnant water under the pan and cause a musty odor. A pro can clear and re-bed the assembly.
- Our Long Beach Plumbing experts recommend switching to a 2-inch shower drain during remodels for faster drainage and less buildup.
- Prevent trap evaporation
- Rarely used guest showers smell because traps dry out. Pour a cup of mineral oil into the drain after filling the trap with water—it slows evaporation.
- If a floor or shower drain is intended as a “primered” drain, ensure the trap primer line is functional.
- Check venting
- Gurgling after the toilet flushes suggests a venting problem or partial blockage downstream.
Laundry and Floor Drain Odors: Special Considerations
- Sanitize the washing machine
- Front-loaders: clean the door gasket, run a “tub clean” cycle with an oxygen-based cleaner, and clear the drain filter.
- Top-loaders: run a hot wash with a machine cleaner. Leave lids/doors ajar to dry.
- Standpipe and trap
- Odors often come from lint-laden biofilm in the standpipe. Dose enzymes overnight and flush with hot water.
- Verify standpipe height (typically 18–30 inches above the trap) and trap depth. An undersized or S-trap can siphon dry.
- Our Long Beach Plumbing experts recommend a 2-inch trap/standpipe for modern high-flow washers.
- Floor drains
- Pour water to refill dry traps. Add a few tablespoons of mineral oil to slow evaporation.
- Confirm cleanout plugs/caps are present and tight; a missing plug can vent sewer gas indoors.
Venting, Mainline, and Sewer Gas: When It’s Not Just the Drain
- Roof vent blockage: Leaves, bird nests, or salt-air corrosion (common near the coast) can restrict vents. If multiple fixtures gurgle, have the roof vent inspected and cleared safely.
- Air admittance valves (AAVs): These under-sink one-way vents fail with age; if you hear frequent whooshing or smell sewer gas near a cabinet, the AAV may need replacement.
- Partial mainline clog: Slow drains house-wide, lower-level odors, or backups point to a root intrusion or offset. A camera inspection can confirm. Our Long Beach Plumbing experts recommend adding two-way cleanouts if you don’t have them.
- Backwater valve: In flood-prone streets, a stuck backwater valve can trap odors. It may need cleaning or replacement.
Important safety note: Strong, persistent rotten-egg odor can indicate hydrogen sulfide from sewer gas. Ventilate the area and avoid open flames. If symptoms like headaches or nausea occur, step outside and call a pro.
Products and Practices to Avoid
- Harsh chemical drain openers: They can damage pipes, septic systems, and disposals—and mixing chemicals (especially with bleach) is dangerous.
- Deodorizers only: Scent covers the symptom without fixing the cause. Always restore the trap seal and remove biofilm.
- Continuous bleach use: Occasional sanitizing is fine, but frequent bleach can harm rubber seals. Our Long Beach Plumbing experts recommend enzyme maintenance for routine care.
Long Beach-Specific Tips
- Coastal humidity accelerates biofilm growth. Monthly enzyme treatments and regular splash guard cleaning go a long way.
- Older housing stock with cast iron or galvanized pipe can develop rough interiors that trap odor-causing debris. Hydro-jetting and selective repiping may be smart investments.
- Drought habits—rarely used guest baths and garage floor drains dry out. Put “run water monthly” on your calendar.
Prevention Checklist (Do This Monthly)
- Run water in rarely used fixtures to keep traps wet.
- Clean stoppers, strainers, and overflows; brush with dish soap.
- Dose enzyme cleaner in kitchen, bath, and laundry drains overnight.
- Wipe garbage disposal splash guard and grind ice/salt.
- Leave washer doors open to dry; run a tub-clean cycle.
- Inspect under-sink traps and valves for dampness or corrosion.
Our Long Beach Plumbing experts recommend snapping quick photos of your traps and cleanouts after you service them—handy reference for future maintenance or if you need to call for help.
When to Call A1 Best Plumbing
- Sewer odor persists after refilling traps and cleaning biofilm.
- Multiple fixtures gurgle or smell, pointing to venting or mainline issues.
- You suspect a failed AAV, missing cleanout cap, or root intrusion.
- You want a camera inspection, hydro-jetting, or to add cleanouts/backwater protection.
A1 Best Plumbing provides same-day diagnostics, enzyme-based maintenance solutions, safe vent and mainline clearing, and long-term fixes our Long Beach Plumbing experts recommend.
We’ll find the source, eliminate the odor, and help you keep it from coming back—professionally and safely.Looking for fresh, odor-free drains that stay that way? Contact A1 Best Plumbing today. We’re your local Long Beach team for clean, quiet, and healthy plumbing.