You can treat your sewer line out to the street!!! It is especially a good idea after you have had a back-up and had the line opened by a drain cleaning professional, even more so if he was not able to get more than one blade through the line. The large cable opens up the line so that it can flow again, there can and usually is a built up blockage of somekind in the line that the cable pushes out. But, what it can't clean out completely is the residue left in the line that accumulates on the walls of the interior of the pipes, it's that old accumulation that helps trap new debris and contributes daily to reducing the diameter of the inside of your drain. That's where Bio-Clean works to help keep your lines free of future back-ups. Adding Bio-Clean to the sewer line will start those good bacteria working to clean out all the organic debris clinging to the walls of that line. How to treat: You can introduce the Bio-Clean to your sewer line via the clean out. This line is much larger than the interionr lines inside your house. You will need 1/2 cup that would be 4oz per 25ft of sewer line. Mix each 1/2 cup treatment with about 1 gallon of warm water and pour it down the clean out. Do this when you won't need to use water in the house for 6 to 8 hours to give Clean Gene and his buddies time to multiply and get a grip on the gunk in your pipe before you start running water down the pipes again. You can also treat your sewer line right from your toilet, if you can't get to the clean out plug. Just pour 1/2 cup of Bio-Clean in the tiolet and flush once for each 25ft of sewer line.( be sure to add the 1/2 cup of Bio-Clean each flush) then don't use andy more water or flush again for 6-8 hours.