We cannot locate the main sewer pipe coming into our house. We have dug down about 3 and a half feet under the concrete floor. On one side we hit dirt, and the other is gravel. The gravel is collapsing into the trench from under the concrete. We can hear the water running through the sewer when we flush the upstairs toilet but with all this digging I.m wondering how far down could the pipe be? Is there some type of radar that can find these pipes?