A clog in one drain only affects that fixture. A main sewer line clog affects several fixtures, and water from one fixture shows up in another. The strongest signs are a tub or shower filling when the toilet is flushed, gurgling toilets, several slow drains at once and water at the outdoor cleanout.
Single-drain clog or main line clog?
Every fixture has its own drain, and those drains join together into the main line. If only one fixture is slow, the clog is almost always in that fixture's drain or trap. If several fixtures in different rooms are slow, the clog is probably where those drains come together, which is the main line.
| Single-drain clog | Main line clog |
|---|---|
| One sink, tub or shower is slow | Two or more fixtures in different rooms are slow |
| Other drains work normally | Water from one fixture appears in another |
| Gurgling only at that drain | Toilets gurgle when other fixtures drain |
| Usually hair, soap or food | Often roots, grease, wipes or pipe damage |
7 warning signs of a main sewer line clog
1. Water comes up in the tub or shower when you flush
Tubs and showers are often the lowest drains in a home. When the main line is blocked, flushed water takes the easiest way out, which is up through the tub drain.
2. Several fixtures are slow at the same time
A slow kitchen sink plus a slow bathtub plus a sluggish toilet usually means one shared blockage, not three separate clogs.
3. Toilets gurgle or bubble
Gurgling when a sink or washer drains means air is being pushed through the toilet's water seal by a partial blockage downstream.
4. The washer makes another drain overflow
A washing machine discharges a lot of water quickly. If that water appears in a floor drain, tub or toilet, the main line cannot keep up.
5. Water at the outdoor cleanout
If you remove the cleanout cap (carefully, since it may be under pressure) and find standing water, the blockage is downstream of that point, between the cleanout and the street.
6. Sewage odors
Persistent sewer smells inside or near the cleanout can mean waste is sitting in the line instead of flowing away.
7. Clogs that keep coming back
If drains clog again shortly after being cleared, the cause may be roots or a pipe defect in the main line. A camera inspection can show it.
A quick at-home check
- Run water in the bathroom sink for a minute and watch the tub and toilet.
- Flush the toilet and watch the tub or shower drain.
- If water rises in another fixture, stop using water and treat it as a main line problem.
What to do next
Stop using water to avoid an overflow. If neighbors are also having problems, contact your city or county sewer agency, because the public main may be involved (see our Whittier sewer lateral guide). Otherwise, call for main sewer line cleaning.
Not sure which drain service you need? Describe the problem and we'll point you in the right direction.
Call (562) 245-5818Frequently asked questions
Can I clear a main line clog myself?
Rental drain machines exist, but main line work involves heavy equipment and sewage exposure. If the line is backing up into the home, most homeowners call a professional.
Will a plunger fix a main line clog?
Usually not. A plunger may move water around but does not reach a blockage in the main line.
Related services
Main Sewer Line Cleaning
Clear main drain and sewer lateral blockages that back up several fixtures at once.
Learn MoreClogged Toilet Repair
Help for toilets that clog, overflow or drain weakly, including main line warning signs.
Learn MoreMore drain guides
- Whittier Sewer Lateral Guide: Who Is Responsible for Your Sewer Line?
- Why Does My Drain Keep Clogging? 8 Common Causes and Fixes
- Hydro Jetting vs. Drain Snaking: Which One Does Your Drain Need?
- Drain or Toilet Backing Up? What to Do Right Now
This guide is general information, not legal or engineering advice. Rules and agency contacts can change; confirm details with the City of Whittier or Los Angeles County Public Works.