Help! Sewer line question for a STR

[Rene K Nelson]

We are under contract to buy a STR property in a mountain town. We completed the inspection yesterday and opted to do the sewer line inspection. One of the findings of the sewer line video from the house to the city sewer line is that a neighbor's sewer line is tapped directly into our sewer line before it meets up with the city sewer line. Is this a common practice? What happens if the line blocks from the tapped in point to the city sewer point? Who's responsible? We don't know if the current neighbor even realizes this. Is this a big problem? Liability? Cause for concern? or a common practice? What do we need to do to protect ourselves from liability?