Drainage underground clay pipe-work pipe work laid from 1900 to 1980s can move due to natural ground movement. All drainage pipe work are connected together by collars, no drainage were laid with just one single pipe, there were always collars which connected one pipe to another.
Collars are the weak point in the drain run, after years of natural ground movement, collars open and effluent flow seeps in to the surrounding sub soil, and eventually there is a void, no support beneath areas of pipe-work.
Mother nature then starts, tree root ingress grow to moisture, so with warm water from baths showers house hold waste, also there is no frost at the depths of running sewers. Drains are then blocked and damaged due to heavy tree root ingress.
All drains should be checked by CCTV Drain Surveys to ascertain the condition, with our drain lining method, to prevent further deterioration to existing pipe-work.