A clean out is a threaded cover that you can remove and snake the sewer line. It's located on the line to the septic tank within 18" from the foundation. You may have to dig around a bit to locate it as dirt can build up over the years. Have hubby check the clean out,( Open the house clean out and flush the toilet at least three times. If the water backed up the blockage is between the clean out and the street., If very little water got past the cleanout then pull a toilet and snake from there.,) before you send him up on the roof. Let me know what he finds. Tom