Who sues for damages

[Shoshana Shulman]

My tenant informed me that the sewer was blocked by someone in a house at the end of the block. Since these are attached row homes all the homes basements are flooding. What do i do? I am out of the country. I do not know the people in the house that caused this. My tenant has tenants insurance because i require it. Who sues whom for damages? How to begin?