Published by All Systems Pros · Updated October 12, 2026
Recognize the Signs of a Sewer Backup
A sewer backup occurs when wastewater cannot flow away from your home and reverses back through your drains. Early signs include gurgling toilets, slow drains, and foul odors coming from your plumbing fixtures.
When the main sewer line is blocked, wastewater seeks the lowest point of entry to escape. Because the plumbing system relies on gravity, this usually means water will back up into ground-floor or basement bathtubs, showers, and floor drains first. If you flush a toilet and water comes up in the shower, or if running the washing machine causes the nearby sink to overflow, the main sewer line is likely obstructed. Recognizing these signs early allows you to stop using water before a minor backup becomes a major flood inside your living space.
- Gurgling sounds from toilets or drains when other fixtures are used
- Water backing up into the shower or tub after flushing a toilet
- Foul sewage odors emanating from drains
- Multiple slow drains occurring simultaneously across the house
Stop the Flow of Water Immediately
Stop using all plumbing fixtures immediately. If safely accessible, shutting off your domestic water supply can help stop household fixtures from adding wastewater; it cannot stop sewage entering from a public-main backup.
Every drop of water that goes down a drain will add to the backup. Do not flush toilets, run the dishwasher, or use the washing machine. If you cannot verify that all household members have stopped using water, locate your main domestic water shutoff valve and turn it off. This valve is typically located near the water meter, in the garage, or on the exterior wall where the water line enters the house. Shutting off the domestic supply can limit water added by household fixtures, but a backup from the public sewer may continue. Report suspected public-main problems to the local sewer authority.
- Turn off all faucets and plumbing fixtures
- Halt all water-using appliances like dishwashers and washing machines
- Use the main domestic water shutoff only if it is safely accessible
- Inform all household members that the plumbing system is out of order
Avoid Contact with Contaminated Water
Stay out of the affected area and do not touch the backup. Sewage contains harmful bacteria and pathogens that pose severe health risks upon contact.
A sewer backup is not clean water. It is highly contaminated wastewater, often referred to as black water, which requires specialized handling. Never walk through, touch, or attempt to clean up raw sewage without proper protective equipment. Keep children and pets far away from the affected rooms. If the backup has reached electrical outlets, appliances, or extension cords, do not enter the room under any circumstances, as the standing water may be electrically charged. Your primary focus must be on safety and isolation, not cleanup or repair.
- Evacuate the immediate area where the backup is occurring
- Keep children and pets away from contaminated water
- Do not enter rooms where water has reached electrical outlets
- Do not attempt to clean up raw sewage yourself
Do Not Attempt DIY Drain Cleaning
Do not use chemical drain cleaners or attempt to clear a main line backup yourself. Chemical cleaners cannot clear solid main line blockages and create hazardous conditions.
Pouring chemical drain cleaners into a backed-up sewer line is ineffective and dangerous. These chemicals can cause severe burns and splash injuries if they back up further or if a plumber later needs to open the line to clear the blockage. Furthermore, standard household plungers or small hand augers are not long enough or powerful enough to reach and clear a blockage in the main sewer lateral. Attempting to force a blockage can damage your pipes or push the obstruction deeper into the system.
- Avoid all chemical drain cleaners due to burn and splash hazards
- Do not use household plungers on main line backups
- Do not insert hand augers into main sewer cleanouts
- Leave the blockage undisturbed until a professional arrives
Understand Sewer Lateral Responsibility
In most local jurisdictions, the property owner is responsible for maintaining the entire sewer lateral pipe from the house to the city main connection.
When a backup occurs, it is important to know who is responsible for the repair. According to local municipal guidelines in Pasadena, Glendale, Monrovia, and unincorporated Los Angeles County, the property owner is generally responsible for the house sewer line all the way to the connection at the public sewer main. This includes clearing blockages and repairing damage, even if the pipe extends beyond the property line into the street. A professional plumber can inspect the line to determine the exact location and cause of the blockage, helping you understand the necessary next steps.
- Property owners maintain the lateral pipe from the house to the city main
- Responsibility often includes the section of pipe under the public street
- Municipalities maintain the main public sewer line only
- A professional inspection is required to pinpoint the blockage location
Call a Professional Plumber
Contact a licensed plumbing professional to diagnose and clear the sewer backup. Specialized equipment like sewer cameras and hydro jetters are required to safely resolve main line blockages.
Resolving a main line sewer backup requires professional intervention. A qualified plumber will typically start by locating the sewer cleanout to access the line safely from the exterior of the home. They can perform a sewer camera inspection to identify whether the backup is caused by tree roots, a collapsed pipe, or a severe clog. Once the cause is identified, they will use appropriate methods, such as hydro jetting or mechanical snaking, to clear the obstruction and restore proper flow. After the line is clear, you can coordinate with a professional mitigation company to safely clean and sanitize the affected areas of your home.
- Locating and accessing the exterior sewer cleanout
- Performing a video camera inspection to diagnose the blockage
- Clearing the line using mechanical augers or hydro jetting
- Verifying flow is restored to the municipal sewer main
Sources and further reading
About All Systems Pros
All Systems Pros is a plumbing service company based in Monrovia, CA. The company lists Rheem ProPartner, A. O. Smith Certified Contractor, and Raypak credentials. These general guides help explain plumbing topics; equipment instructions and project requirements must be checked for the specific property.
