Signs the blockage is in the main line
- Flushing a toilet makes water rise in the tub or shower.
- The basement floor drain overflows when the washing machine drains.
- Several drains are slow at once, especially on the lowest floor.
- Gurgling from a drain when another fixture is used.
- Sewage or gray water appears in the lowest drain after heavy rain.
Do this now
Stop all water use
No flushing, laundry, dishwasher or showers. Everything you send down can come back up at the lowest drain.
Keep away from the water
Treat it as contaminated. Keep children and pets out of the area.
Find the cleanout
A capped pipe, usually outside near the foundation or in the basement. Knowing where it is speeds up the visit. Don't open it yourself while the line is full; it can release sewage under pressure.
What blocks a main line
Tree roots
Most commonTell: Older clay or cast iron pipe; backups that recur every year or two.
Fix: Cable or jet the line, then a camera to judge the pipe. See hydro jetting.
Wipes and paper products
Most commonTell: Sudden backup; no history of trouble.
Fix: Clearing the line, plus not flushing wipes.
Grease buildup
PossibleTell: Gradual slowing, worse at the kitchen end.
Fix: Jetting removes it from the pipe walls.
Sagging or broken pipe
PossibleTell: Clogs return within weeks no matter how it's cleaned.
Fix: Camera inspection, then a spot repair or replacement.
City sewer surcharge
Less commonTell: Backup during heavy rain; neighbors affected.
Fix: Report it to the sewer utility; a backwater valve prevents repeats.
What clearing it looks like
A plumber opens the main cleanout, lets the line drain if it can, and runs a cable machine through to the blockage. Recovering what's on the cable, such as roots, wipes or grease, tells you a lot about the cause.
If the line has backed up before, ask for a camera inspection afterwards. It shows whether the pipe is damaged, which decides whether the next step is maintenance cleaning or a sewer line repair.
Call now if
- Sewage is in the house.
- Water is backing up and you can't stop using fixtures (a household with no second bathroom, for example).
- The backup happened during heavy rain and may come back with the next storm.
More questions
Who pays if the city sewer caused my backup?
Rules differ by city. Report it to your sewer utility right away and ask about its claims process. Problems in your own lateral are usually the owner's responsibility.
Will plunging fix a main line clog?
No. Plunging can push water out of another fixture. The main line needs to be cleared from a cleanout.