A backslope in a drainage line from day one is bad workmanship. Over the years it might settle a little more and become worse.
THe question is not that of harboring bugs. It's a matter of degraded capacity of the pipe.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.