Pitch fibre was a material widely used in the 1960’s to construct underground drain pipework. Its serviceable lifespan is only expected to last 40 years and it is prone to sudden failure and no longer used. Any drain pipes made of pitch fibre should be replaced as soon as possible.
Further advice may be obtained from a suitably qualified person, such as a N.A.D.C [National Association of Drainage Contractors] registered specialist drainage contractor.