Toilet Backups: Common Causes and Sewer vs. Drain

When a toilet keeps backing up, it can be frightening and inconvenient. The most common causes are blockages or plumbing issues within your home’s drain system, but in some cases the problem originates outside—at the sewer main—meaning it’s handled differently than typical household clogs.

Below are the most frequent reasons toilets back up, plus clear indicators that the issue may be a sewer problem rather than an internal drain blockage.