My question involves real estate located in the State of: Massachusetts
We own a 2-family house, and live upstairs, with tenants on the first floor. Behind our house there is an 8-unit apartment building whose sewer line runs just under our basement floor. This line is degraded and broken and has been flooding our basement up through the floor with sewage for 7 weeks now (after seeping for many years). The property owner (actually, her son) is almost entirely unresponsive and is unwilling to fix the pipe; his building is uphill of us and his tenants are apparently unaffected.
This apartment building was constructed (with no building permit) in about 1950 on the site of an old (~1850) frame house, and they picked up the old sewer line, a 4-inch Akron clay pipe meant for 2 toilets and 2 sinks. Our house was built in 1885 on top of this line, which was laid in 1882 just before the property was subdivided. We have had a full title search done and there is no mention anywhere of the sewer line, except for a sketch and the original permit from 1882 in the city engineering department's records. Our line is now independent down to the point where they join under our front porch; our interior line and the shared pipe from the front of our house to the main sewer in the street are 5 years old and work perfectly, because we had them replaced (for $10K, which we paid) before we knew we had any connection whatsoever to the apartment building. There is no longer any necessity for his line to run 150 feet back under our house, because for at least 120 years there has been a main sewer line in the next street up, just in front of the apartment building.
The city engineer, law department and board of health are sympathetic, but claim they have no jurisdiction because it's a private line. I have been warned that if I break down and pay to have his pipe fixed, not only will I be out all the cost of the work (more like $15-20K this time), but that it may make me responsible for this pipe and any damage it causes forever, and strengthen his implied easement.
What can I do? Is there really no way for me to make him repair or move his pipe?
Many thanks for any advice.

