Calling pros to solve a mistery that I or a plumber with 20 years of expierence could not solve. We bought a house over a year ago. The owner passed away, some time ago, so we were not able to ask questions that could have helped solving this. We live on a mountain. Gravity fed septic system. Recently we had snow thaw and a lot of water came from the mountain. Basement was dry, but I was able to hear the water running inside the main sewer pipe even when nobody was using water. All the plumbing seems to be standard exept for one instance, which is completely driving me nuts. Please see photo. There is a sealed sump pump and pipe running in a "T" from it. One end runs along garage wall on a slope and through the wall and connects to an elbow of rain gutter pipe that exits about 25 feet from the house to the rain drainage. And then the second end of the "T" (which is MOST likely my mystery) goes up through garage wall and connects to an extension that is used only by a small laundry sink. When laundry sink is used, water flows through the main sewege line. Sump pump is dead, it never worked, but when I started investigating where water was entering sewer pipe I went to that pump and could feel that water was running through the pipe, as it seemed to me was circulating in that T fitting and if I am not mistaken was going up, as if pressure was pushing it up to the sewer line. Again, sump did not work and the peat where the sump pump is located was dry. The only probable cause that I could think of is that previous owner had burried drainage that somehow connected to the gutter runoff pipe and the pressure was so great (our mountain is steep) that it pushed water up the gutter runoff pipe into the pipe that runs through our garage, entered "T" fitting circulated there, went 4 feet up and entered sewer line. I am sorry for the long essay, but I would sincerely appriciate if somebody can shine a light for me on two questions. 1) why would somebody connect the second end of T from sump to the sewer? 2) Could I be right about under-ground water that could have pushed itself up the slope? Please help. Thank you, Mike.