Neighbor connected to our property's sewer line

[Maureen M.]

Hello - We just purchased an investment property to fix n' flip. We knew we had to repair a section of the sewer line. The contractor re-scoped the line and we now see that a neighbor's sewer is connected to our line which then runs directly to the main sewer line. This house is in Denver, CO. Per Denver code, each building must have its own separate line to the main sewer line.  I think we need to inform the neighbor that they need to disconnect from our line and install their own separate line to the City's main sewer. I'm not seeking any conflict with the neighbor but when we sell the house, we do not want any issues during a buyer's inspection. Also, we have to repair the portion of the line that they are connected to. I question also if we should be requesting them to pay for a portion of the repair? Any thoughts or advice appreciated. Thanks!