Quick answer
A main sewer line clog shows up first at the drains nearest the floor: several fixtures slow at once, water rising in the tub or shower when a toilet is flushed, or a floor drain backing up when the washer empties. Stop using water in the house, skip chemical drain cleaner, and call a plumber with a sewer machine; the cleanout lets them clear it without pulling a toilet. If neighbors are backing up too, call the city. HomeServe puts a main-line clog at $150–$500. Call (888) 217-6781 to reach a plumbing company taking calls in your ZIP.
Follow the short menu, then your 5-digit ZIP. The line goes quiet for a few seconds while it connects; stay on. If it does not connect, call once more: companies taking calls change minute to minute.
Written & reviewed by Marcus ReedIICRC WRT
Reviewed October 27, 2026· Next review Apr 2027
A clog in one drain affects one fixture. A clog in the main sewer line affects the whole house, and it shows itself first at the drains nearest the floor: basement, ground-floor shower and floor drains: water backing up into a shower or floor drain when the toilet is flushed or the washer empties. If that is what you are seeing, stop using water in the house now, because everything that goes down the drains will come back up out of the drain nearest the floor.
Signs It Is the Main Line, Not One Drain
- More than one fixture is slow at the same time, especially toilets, tubs and showers together.
- Flushing a toilet makes water rise in the tub or shower, or gurgle in a sink.
- Running the washer makes a floor drain or a basement toilet back up.
- Water or sewage appears at the cleanout (a capped pipe, usually near the foundation or in the basement).
What to Do Right Now
- 1Stop all water use. No flushing, no laundry, no dishwasher, no showers, for everyone in the house.
- 2Do not use chemical drain cleaner. It rarely reaches a main-line clog and leaves caustic water in the pipe for whoever opens it next.
- 3Find the cleanout. If you can see it, the plumber can usually clear the line from there without pulling a toilet.
- 4Keep people and pets away from any backed-up water. Sewage is contaminated water.
Talk to a plumber about this
One call reaches a plumbing company taking calls in your ZIP.
Who Fixes What
| What is happening | Likely cause | Who to call |
|---|---|---|
| Whole house slow, no backup yet | Main-line clog: roots, grease, wipes | Plumber with a sewer machine |
| Clogs keep coming back every few months | Roots in a joint, a sag (belly) or a broken pipe | Plumber with a camera inspection |
| Backup only after heavy rain | Groundwater getting into the line, or the city sewer | Plumber, and report it to the city |
| Neighbors backing up too | City main | Your city or sewer utility |
| Sewage on floors or carpet | The backup has already reached the house | Plumber for the line, then a water damage company for cleanup |
What a Repair Costs
HomeServe puts a main-line clog at $150–$500 and routine drain cleaning at $100–$275. Repeated clogs usually lead to a camera inspection to see whether the pipe itself is damaged. The drain cleaning page shows the sources, and our guide on a floor drain backing up covers what to do if sewage is already on the floor.
When to Call
Call as soon as more than one fixture is affected, and before anyone uses water again. (888) 217-6781 connects you to a plumbing company taking calls in your ZIP. Follow the short menu, enter your 5-digit ZIP and stay on while it connects; if it does not connect, call once more, because the companies taking calls change minute to minute.
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Frequently Asked Questions
How do I know if my main sewer line is clogged?
More than one drain is slow at the same time, flushing a toilet makes water rise in a tub or shower, or a floor drain backs up when the washer drains.
Who do I call for a clogged sewer line?
A plumber with a sewer machine and, for repeat clogs, a camera. If neighbors are backing up too, call your city or sewer utility.
How much does it cost to unclog a main sewer line?
HomeServe puts a main-line clog at $150–$500, against $100–$275 for routine drain cleaning.
Why does my main sewer line keep clogging?
Repeat clogs usually mean roots in a joint, a sag in the pipe or a break. A camera inspection shows which.
Sources
Methodology: How we source and verify data · Report an error
Disclaimer: HearthDry is an independent educational resource. This article is for informational purposes only and does not constitute professional, legal, or insurance advice. Consult licensed professionals before making decisions about your property or insurance claims.
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