Immediate steps
Stop using water in the house. Keep people and pets away from sewage. If electrical outlets or appliances are affected, avoid the area until it is safe.
If you are unsure whether the blockage is in the public main or your private service line, call the city utility or public works number when available.
After flow is restored
Cleaning the line may solve the immediate backup, but repeat problems need diagnosis. Ask whether roots, grease, pipe failure, or a belly caused the blockage.
If sewage entered finished space, cleanup and drying may be separate from sewer repair.
When to treat this as urgent
If sewage is coming up through a floor drain, shower, tub, or basement toilet, stop using water in the house and get help quickly. Do not run laundry, dishwashers, showers, or extra toilet flushes until the blockage is understood.
If only one sink or toilet is slow, the issue may be inside the home. If several fixtures are slow or the lowest drain backs up first, the main sewer line is more likely involved.
What to ask before approving work
Ask whether the contractor has camera evidence, where the defect is located, whether cleaning alone is enough, and whether repair or full replacement is being recommended.
For expensive work, ask for a written scope that explains access points, restoration, permits, expected timeline, warranty, and whether trenchless repair is possible.