Glad this is not my problem !!!

Tried to figure this one out, but have not a clue as how this is happening. Neighbor has an old house with a septic system that is at least 50 years old. That age is on the conservative side ! He has old drain tile in the basement on 2 sides of the basement ; with a drain tile running from one of those sections to the Sump Pit. He is soon to get a new Septic system put in, but can't figure out how toilet paper is backflowing from the floor drain tile, into the sump pit.


Any ideas as to how this could be happening ?