Steps For How to Clear A Main Sewer Line Clog Loosen the Drain Pipe Cap (aka Sewer Cleanout Pipe) ... Remove Cleanout Cap, Allow Water to Backflow to Opening. ... Insert the Snake into the Sewer Line Pipe Opening. ... Run the Tool Until All Clogs are Gone. ... Clean Up and Replace Sewer Cleanout Cap (Don't overtighten.) Mar 20, 2019