aborvitea dilema part 2

Kimberly, thanks for your quick response to my question. I am curious also as to whether or not the root system is a threat to my septic tank. The trunk is about 20 feet from the tank, and where the plumbing comes out of the house to the tank is about 8 feet from the trunk and 4 feet down from the ground surface. You mentioned cutting and pulling out the "mother root" in last response... If cutting it down is my safest option, how will I be sure that we get all of it and not worry about the septic situation?