Yesterday (Friday the 13th) we had the sewer scoped and located by a rooter company (under $200.00).
That's great! Now that it's marked on the surface and the rooter company has accepted the liability for the location in writing, we can move on to the next item.

If you read my 1st post - no easement has been recorded - Is this a case of a "Prescriptive easement"?
If you have researched the title back 80 years, not just at the register of deeds, but all of the other places official documents can be found, you will know whether a recorded easement exists. But a written easement of that age would not have to be recorded. Many were not, but just kept on file at the grantee's office. We still don't know who operates the sewer system.

If there is no recorded or unrecorded written easement, then you have a prescriptive easement. In that situation you will need to look to the case law in your state to see what courts have historically done in determining the with of prescriptive sewer easements such as yours. Or you could just ask whoever operates the sewer system you use. They will probably know the answer to your other questions.