Every drain in a house eventually joins one main line that leaves the building as the sewer lateral and runs to the public sewer. When that line is blocked, water has nowhere to go, so it rises to the lowest opening it can find. In a single-story slab home, that is often the tub or shower, which sits lower than the toilet rim.
Because a toilet releases a large volume of water at once, flushing is often what reveals the blockage. Plunging the toilet does not help and can push more water into the tub.
Likely causes of a main line backup
| Cause | Why it is common |
|---|---|
| Tree roots | Roots enter cast-iron or clay laterals at joints and cracks, especially near mature trees |
| Grease and wipes | They build up and catch other debris over time |
| Pipe sag or offset joint | Older laterals can shift, leaving low spots where waste settles |
| Scale in cast iron | Interior corrosion narrows the pipe |
| Blockage on the public side | Sometimes the problem is beyond the property; check with the city |
What a plumber usually does
Find the cleanout
The plumber locates the sewer cleanout, often outside near the foundation, to reach the main line without going through a fixture.
Relieve the pressure
Opening the cleanout may release backed-up water outside rather than inside, which is safer for the house.
Clear the line
A drain cable or other method is used to open the blockage, and what comes back on the cable hints at the cause.
Inspect with a camera
A camera inspection can show roots, cracks, sags or breaks and where along the lateral they are.
Explain options
Depending on what is found, options range from routine cleaning to repairing a section of the lateral.
The first hours
- Immediately
- Stop all water use and keep people away from the sewage.
- Next
- Call a licensed plumber and describe which fixtures backed up and when.
- While waiting
- Take photos for your records and remove belongings from wet areas if it is safe to do so.
- After the line is cleared
- Clean and disinfect affected surfaces, or consider a cleanup professional for larger spills.
- Afterward
- Ask about a camera inspection to understand the cause before it happens again.
Questions to ask
- Where was the blockage, and what caused it?
- Can I see the camera footage?
- Is the problem on my side of the lateral or the public side?
- What are the options for preventing a repeat, and what does each involve?
- Can I have the price for the recommended work in writing?
Common questions
Should I keep plunging the toilet?
No. If water is coming up in another fixture, the blockage is in the shared line and plunging only pushes water around.
Who is responsible for the sewer lateral?
Responsibility for different parts of the lateral can vary. Check with the city about which section is yours.
Can I use the toilet after the line is cleared?
Yes, once the plumber confirms the line is flowing. If roots or damage were found, ask how soon it may need attention again.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.