They have something to put in to kill the roots but the only efective way to use it is block your sewer and fill it up, but it dont get the roots outside sewer and they come back, only way to get rid of them is to find the source and destroy it, You can have a cable run in it but they come back, dig up sewer and install PVC sewer pipe.
A major problem with clay sewer pipe (besides its fragility) is its vulnerability to root intrusion.
In my opinion, once you have a problem with root intrusion you have only two good permanent options: 1) kill the invaders (with a root herbicide and/or clearing the offending trees from the property); or, 2) replacing the vulnerable clay line with something much more impervious to root invasion. In my opinion, the most impervious replacement is polyethelene pipe, preferably seamless, installed via the “trenchless” method.
Copper sulphate. Will slow down the growth. But the only true fix is to replace the pipe
All advice is given with-out seeing the job, and hence all advice MUST be taken as advice with limited knowledge on the exact situation. NO responsibility can or will be taken. And yes, I am a licensed Plumber and Drainer with my own business in Brisbane Australia.