When setting up a filtration system, the inlet/outlet require a threaded fitting; but after that I could continue to use threaded PVC fittings or solvent-weld fittings. My question is which is better. Should I put my PVC pipes together with more threaded PVC fittings vs solvent-weld fittings? For example, I am installing two water filters and I thought of using Unions, but those Unions come with or without threads. Which is better?
