Your first steps after a sewage backup
If sewage backs up, stop using the water and toilets that drain to the affected area, keep everyone — especially children and pets — away from it, avoid contact with the sewage, and contact your landlord's emergency maintenance immediately.
Raw sewage carries germs, so do not try to clean up a large backup yourself without protection. Turning off water use that adds to the backup can help, and ventilating the area is wise if you can do it safely. Move belongings out of the sewage's reach, then take photos and video and report it in writing as an emergency.
Because sewage backups involve the plumbing and pose a real health risk, professional cleanup and the repair are generally the landlord's responsibility, not yours. If your landlord fails to respond to a sewage backup, a free review can help you decide what to do next.
This is general information about California tenant rights, not legal advice. Every situation is different.