Possible Easement Issue
I purchased a rental property in 2018 that was a totally normal real estate transaction with no existing easements or irregularities mentioned.
During the reno I found out that back in the 50's when the house was built, the city (presumably) had run the sewer line out of my back yard and tied it in with our neighbor's sewer line, and then run it out to the main line on a side street, rather than running each sewer line up to the main at the street our address is on. (i.e. I'm one lot away from a corner lot, and our sewer runs through the corner lot to hit the side street.)
Anyway, a while back I had messaged the owner of the house next door to introduce myself, and just last night he replied to my message basically saying our sewer line runs through his property and he never gave us an easement to do that, nor does he know of one that exists. I'm fairly certain both houses and their respective sewer lines were in place prior to either of us owning these houses, but I have a very limited knowledge of how all that works legally.
Googling this scenario was unsuccessful. Any recommendations on how I should proceed in the event that this guy decides to try and be a headache?