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.
One of the most dreaded phone calls a homeowner can make involves the phrase septic clog
Find your home's main sewer cleanout (a white PVC pipe with a cap sticking out of the ground near the house foundation). Remove the cap. Use a heavy-duty toilet auger or a 50-foot sewer snake