The Department of Public Works maintains the City main sewers on a regular basis to assure that flows are unrestricted.  If your home experiences sewer back-up, you can call Public Works to have the line power jetted.  In order for Public Works to power jet the line, there must be an external clean out available.  Common causes of sewer back-ups are tree roots or other blockage.  If the problems continue on a regular basis, we recommend having it checked by an insured plumbing/sewer contractor )permits are required).  The City is not responsible for the sewer line from your home to the City main.