Foaming Root Killer works in both septic and city sewer lines. If you have a septic tank and the root infiltration is either in the main waste line (the line that brings sewage to your septic tank) or in the tank itself, then you should use Roebic Foaming Root Killer (FRK) to kill those invading roots that can cause backups to the system. If you have roots that are clogging a sewer line, then you may have a potentially costly problem. Roebic Foaming Root Killer is unique - it does not contain copper sulfate. Foaming Root Killer contains dichlobenil which kills the roots and prevents new growth. New root growths from outside the pipe joints are retarded or inhibited when they come in contact with the dichlobenil inside the pipe. FRK self-foams on contact with water. The foam acts as a carrying agent, putting the active ingredient in contact with the tree roots above the flow. FRK also contains ingredients that help speed up the decay process of the roots it kills, this enables you to experience fast relief from your root problems. (It should take Foaming Root Killer, from 2 days to 1 week to clear your line). Your system must have some flow in order for the Foaming Root Killer to work properly. If the Foaming Root Killer cannot get to the roots, it cannot kill them. It's recommended to repeat treatment twice a year.