This European standard specifies requirements for perforated pipes and compatible fittings made from vitrified clay with or without sockets for the construction of French drains , land drains and drainage of waste tips. They may also be used for percolation into the ground. Fittings need not be perforated . Where this standard provides for different strength classes or areas of perforations the specifiers purchasers may select according to their requirements. Preferred angles are given for bends and junctions but other values are acceptable.