I have a jebao1200 that I need to plumb. The return is 1.5 inches wide. Do I want to use the white pvc female adapter with tapered threads or the grey female pvc adapter with non tapered threads? I think the threading on this is metric? I think once I get either on I am not getting it off so I am trying to figure out which will give a water tight seal. I also have a gasket to that will go between the fitting and the pump.