Why don't you use a cam-lock or cam and groove coupling? You can buy them with NPT fittings so they will be really easy to couple to PVC or CPVC, and they come in everything from polypropylene to stainless, and they come range from 1/2" up. You can get them anywhere from Amazon to McMaster. To adapt from a straight pipe, get an appropriate sized socket to NPT adapter and solvent weld it to the end of your pipe, then you can use NPT fittings. I think you can even buy cam-lock fittings that have a socket meant for welding directly on to a pipe.