Odor after main line work

Quick Answer:

If you notice a persistent sewer-like smell while ventilating after recent main line work, start by locating where the smell is strongest, top up water in every trap, and inspect any fresh connections or the cleanout cap for loose seals. If the smell continues after those checks, ask the crew or a plumber for a targeted camera inspection of the repaired section to find leaking joints or a cracked pipe.

Why This Happens

Work on a sewer or main line can disturb seals, displace trap water, or leave a cleanout cap loose. Any opening in the sewer system can allow sewer gas to enter your home. In some cases the odor comes from dry traps (no water seal), in others from a poorly seated cleanout cap or a new connection that wasn’t tightened or gaskets weren’t installed correctly. Less commonly, a repaired section can have a small leak or a cracked fitting that emits gas only under certain conditions.

Step-by-Step What to Do

1. Pinpoint where the smell is strongest

Walk through the house with windows open to cross-check. Note whether the odor is strongest at a specific fixture (sink, shower, floor drain), the cleanout, or the vent stack on the roof.
Concentrating on where the smell is strongest narrows whether the issue is a local trap seal, a nearby connection, or the mainline repair area.

2. Check and reseat trap water seals

Check every trap-fed fixture (sinks, tubs, showers, floor drains, toilets). If a fixture is rarely used, the trap can dry out—pour a cup or two of water into each trap to re-establish the seal.
For floor drains and seldom-used sinks, add water and, if available, a little vegetable oil on top of the water to slow evaporation.

3. Inspect the cleanout and recent connections

Locate the main cleanout (usually near the foundation or in the yard). Check the cap for proper seating and tightness; look for visible gaps, worn threads, or missing gaskets.
Inspect any fresh connections the crew made: joints should be snug, gaskets present, and seals not visibly damaged. If a fitting looks loose or you see dampness around it, that’s a likely source.

4. If odor persists, get a focused camera inspection

If traps are reseated and caps checked but the smell remains, request a camera inspection aimed at the repaired section. A camera can reveal a leaking joint, a cracked pipe, or a gap where two pipes meet.
Ask the contractor or plumber to run the camera both upstream and downstream of the repair to identify the exact source of the gas escape.

As you go through these steps, keep notes about where the smell is strongest and any visual signs you find—this speeds up diagnosis for a pro.

What Not to Do

Avoid relying on room deodorants or masking sprays — they do not address gas escapes and can conceal warning signs.
Do not ignore a smell that returns after you’ve refilled traps; persistent odor can mean a poor seal or a cracked pipe that needs repair.
Don’t open or disturb exposed joints beyond a basic visual check unless you are qualified—improper handling can make a small leak worse.
Call a pro when the odor persists after traps are reseated, you detect gas at the cleanout, or work involves exposed joints; these are signs that professional repair or testing is needed.

When to Call a Professional

If the smell is strongest at the cleanout or you find a cap that won’t seat properly, call the crew that did the work or a licensed plumber.
If a targeted camera inspection is needed to locate a leak, ask for a plumber with a camera or have the contractor provide one.
If you notice damp soil near outdoor joints, continuous bubbling in traps, or repeated odors despite reseating traps and caps, schedule a professional inspection and repair.

Safety Notes

Ventilate the area while you investigate—open windows and run fans away from the house to push air out.
Sewer gas usually smells unpleasant but is generally not flammable at typical household concentrations. Still, if you suspect natural gas (strong persistent “rotten egg” smell, hissing sound, or multiple pilot lights out), leave the property immediately and contact your gas utility or emergency services.
If you feel dizzy, nauseated, or experience headaches, leave the house and seek fresh air; prolonged exposure to sewer gas can cause symptoms in some people.
Do not use open flames or electrical switches in areas where you suspect a gas leak until the source is confirmed and safe.

Common Homeowner Questions

Will pouring bleach down drains stop the smell?
No. Bleach can temporarily mask odors and won’t fix a gas escape; it may harm pipes or plumbing seals if used repeatedly.
Can a dry trap cause a sewer smell even after main line work?
Yes. Traps that were emptied during repairs or that sit unused can dry out and let sewer gas into the house; adding water restores the seal.
How fast can a camera inspection find a leaking joint?
A qualified plumber can usually locate a leak with a focused camera run in one visit, as long as the camera reaches the repaired section.

For recurring or strong odors after repairs, documenting what you found and asking for a camera inspection of the repair area is the most reliable next step.

main line odor and Drain smells after snaking