Section 192.373 - Service lines: Cast iron and ductile iron(a) Cast or ductile iron pipe less than 6 inches (152 millimeters) in diameter may not be installed for service lines.(b) If cast iron pipe or ductile iron pipe is installed for use as a service line, the part of the service line which extends through the building wall must be of steel pipe.(c) A cast iron or ductile iron service line may not be installed in unstable soil or under a building.35 FR 13257, Aug. 19, 1970, as amended by Amdt. 192-85, 63 FR 37503, July 13, 1998