John, I get your point and agree with your concept. In some cases though, the code requires us to inspect for a Listing. Such is the case with RMC. I don't have access to the ASTM standards but seem to remember that RMC is not tested for internal pressure. Similarly, plumbers PVC is not tested for crush resistivity. Since these products are only tested and Listed for their respective application they are not appropriate for other use.
George
