Abstract: The reusable coupling assembly of the present invention includes a receiving and an inserted section. The tubing engagement end of both the inserted and the receiving sections is constructed and arranged to securely fit around the resin liner in externally threaded fiberglass resin lined metal pipe or tubing with cement mortar backing. When the sections of externally threaded fiberglass resin lined pipe or tubing sections with cement mortar backing are put together utilizing and internally threaded coupling, the receiving and the inserted mating sections come together within a mastic material to prevent corrosive fluids flowing through the externally threaded metal tubing or pipe sections from damaging any exposed metal surfaces within the internally threaded coupling.