Why Does Sewage Smell Come and Go Inside a House?

Each sink, shower, and floor drain has a curved pipe called a trap that holds water. That water blocks sewer gases from rising into your living space. If a drain goes unused for weeks, the water evaporates, especially in dry seasons or heated homes. Then odors slip through until you run water and refill the trap.

You may notice the smell strongest near a specific fixture, like a guest bathroom sink or a basement floor drain. Pour a cup of water down any drain that you rarely use, and the smell often disappears within a day. If it returns, the trap may have a crack or a poor seal that needs a pro's attention.

• Run water in infrequently used drains monthly
• Check under sinks for slow drips that dry traps
• Pour a small amount of water into floor drains regularly
• Listen for gurgling sounds when water drains, which hints at vent issues

A small crack or loose joint in a sewer pipe can let sewage gases escape into your crawl space, basement, or wall cavity. These leaks often come and go because soil moisture, temperature, and air pressure change how much gas seeps through. The smell may be stronger after heavy rain or when the heating system runs.

If the odor is persistent but not constant, check for damp spots, mold, or unusually green grass near the sewer line outside. A slow leak can worsen over time, leading to more serious damage. A local water damage pro can help locate the source and advise on the next steps.

If the smell persists after you refill traps and check vents, it is time to bring in local water damage pros. They have tools to inspect sewer lines with cameras and can pinpoint leaks or blockages without tearing up your floors. Acting quickly can prevent sewage from backing up into your home.

Sewage contains harmful bacteria, so avoid cleaning large spills yourself. If you notice wet carpets, stained drywall, or a strong odor near a toilet, keep the area dry and ventilated. The pros can handle cleanup, drying, and repairs, and they can advise on whether your insurance might cover the damage. Policies vary, and your insurer decides what is covered.

• Call if you see sewage backing up into drains
• Seek help if the smell lasts more than a few days
• Avoid touching sewage with bare skin
• Turn off water to the affected fixture if safe
• Open windows for ventilation while waiting
• Keep children and pets away from affected areas