Why sewage backups usually fall on the landlord
In most cases, yes. A California landlord is generally responsible for sewage backups, because maintaining the plumbing and sewer lines and keeping the home sanitary are the landlord's duties.
Backups usually come from problems in the main sewer line, aging pipes, tree roots, or shared plumbing — all part of the building the landlord must maintain. Cleaning up the sewage and repairing the cause typically falls to the landlord.
The main exception is when a tenant clearly caused the clog, such as by flushing items that do not belong in a toilet. But ordinary sewer and plumbing failures, and anything in the shared main line, are the landlord's responsibility. If a landlord is trying to blame you for a backup that came from the building's plumbing, a free review can help you understand who is actually responsible.
This is general information about California tenant rights, not legal advice. Every situation is different.