The outside diameter of cast iron waste piping is not the same as plastic DWV piping. However, several fittings manufacturers make a plastic adapter fitting with an outside diameter on the hub-less end to match cast iron pipe, thus arranging for the use of the patented no-hub connector (CISPI Designation 310-78). Some code bodies accept the patented no-hub connector as a transition of cast iron to plastic without the use of the plastic adapter fitting. Also, some code bodies accept various flexible connectors for the transition within the connector, thus eliminating the need of the plastic adapter fitting.

These methods of transition have been in use for several years and have proven adequate when the manufacturer's recommendations and the applicable code regulations are followed.

This bulletin is to provide the above background and to state that when connecting plastic DWV to plain-end cast iron pipe, only approved types of flexible joints, couplings, bushings and adapters, designed for the specific transition intended, should be used. Be certain that these flexible joints, bushings, couplings, and adapters are not made of flexible materials or elastomers that can cause cracking or crazing of plastic piping. Where the administrative authority accepts transition connectors without matching outside diameters of the pipes, the plastic adapter fittings are not being installed.

NOTE:
This PPFA User Bulletin is designed to provide guidance in achieving the efficient, effective and informed use of plastic pipe. The suggestions and advice contained in this Bulletin are offered merely to provide plastic pipe users with a general frame of reference. Because specific situations may, and often do require special treatment, the suggestions and advice are obviously not universally applicable. Therefore, the user should carefully assess the requirements of his specific situation before making practical application of anything contained in this publication.