Multiple drains backing up at once

Symptoms

• Toilet, tub, or floor drain backs up when another fixture is used
• Lowest drains in the house are affected first
• Water may back up into a tub or shower when the toilet flushes
• Slow drainage across several fixtures simultaneously

Likely causes

• CommonMain sewer line blockageA clog in the main line backs up into whichever fixtures sit lowest or closest to it.
• CommonTree roots infiltrating the sewer lineA frequent cause of recurring main line blockages in older homes with mature trees nearby.
• PossibleCollapsed or damaged section of sewer pipeOlder clay or cast iron pipe can crack or collapse over time.
• Less commonMunicipal sewer line issueIn rare cases the blockage is on the city's side rather than the home's.

What to do

1. Stop using all drains and toilets in the house until the issue is diagnosed, to avoid worsening a backup.
2. Identify the lowest drain in the house (often a basement floor drain or the lowest-level toilet), since that's usually the first to back up and a good place to check the source.
3. Do not run additional water down any drain while troubleshooting a suspected main line clog.
4. If comfortable doing so, locate the home's sewer cleanout (a capped pipe usually near the foundation or in the yard) for a plumber to access.
5. Avoid using chemical drain cleaners for a suspected main line clog, since they're ineffective at that depth and can create hazards for whoever clears the line.
6. Contact a plumber to snake or camera-inspect the main line, since this generally isn't a DIY-friendly repair given the length and depth of the line.

When to call a pro

Call a plumber promptly for a suspected main sewer line blockage, since it typically requires a motorized snake or camera inspection beyond typical home tools.

Safety