A snake pokes a hole in the clog; a hydro-jet (high-pressure water) cleans the pipe walls completely. For septic clogs caused by grease, hydro-jetting is superior.
If water gushes out of the cleanout when you run a toilet inside, the clog is between the house and the tank. septic clog
Use a heavy-duty toilet auger or a 50-foot sewer snake. Feed it toward the septic tank. When you hit resistance, rotate the snake to break up the wipe/grease mass. A snake pokes a hole in the clog;