I've got some PCV pipe (90mm) that roots have managed to find their way into. A few larger roots through the middle (half a dozen 5mm to 10mm roots) with the rest of the pipe full of fine roots.
What is the best way to remove the roots, without digging up all the pipes and replacing them, as only sections can be easily replaced. I have removed the offending trees so the roots are no longer feeding anything.
What about something like Caustic Soda?