What I've been told for my area is that the sewer pipe running to the street enters the house at a point parallel to the incoming water line, but under the basement. I also assume it runs directly from the entry point to the main soil stack. Using those two points I have a fairly good idea of where the main sewer pipe runs under the basement floor.

My approach would be more complicated if I had multiple soil stacks, since I wouldn't be able to see how the lines fit together under the floor.

Bruce

Do you have access to infrared camera? That actually might be an idea if you are determined to do this.

Another similar idea is a metal drain snake and a metal detector - if your floor doesn't have rebar in it.

Of course a 3/4 PVC drain line along the wall to the floor drain is workable solution that you see often also. Beats jack hammering the floor and tapping into cast iron or clay pipe.

Thanks for the suggestions, if I had a floor drain or only one main stack I'd be in great shape, but I don't.

If I was worried about the pump, I'd sit it another pan with a $10 water alarm at it's side. If it ever fails, I'd hear it.