Find out who is legally responsible for this sewer line: generally, if the line is on the neighors' property, they are; if it's on/under public property, the town or county. Whomever is legally responsible for it must fix it; if they don't, you can sue them for a court order requring them to make the repairs and and for compensation for having lived with sewage and lost use of your space. (If the break is on your property, however, you would most likely have to pay for the fix; it would be your responsibility, generally.)You should be able to find out who is responsible for the broken stretch of line from the county or town clerk or building department. You are advised to retain an attorney to help-- a lawsuit like this more complex than, say, suing someone in small claims over a fender bender or an unpaid invoice, and a layperson (non-lawyer) may have difficulty with the case.