Sounds like you have a blockage between the house and the septic tank. Which would involve using a large power rodder to clear the blockage. In that case I would recommend calling a pro that deals with septic tanks as well as rodding. I could not in the name of your safety recommend you try to power rod you sewer yourself. The machine needed is heavy and dangerous to us to an untrained person. People have lost limbs and or life using these machines.