Plumber Manhattan Beach
Are those Copper x MIP adapters or FIP adapters? Hard to tell.
I can't stand any threaded transition from metal to plastic. But if you HAVE to, the best is to use a Copper x FIP with a plastic x MIP threading into it, but this is only if there will be very little temperature change. If you are going to see wide swings in temperature change, then you must use the plastic FIP that is pre-stressed with a metal ring and screw a Copper/metal x MIP into it, or if they make a plastic by MIP where the MIP is some type of metal i.e. brass into a metal x FIP.
Also, many plastic manufacturers are extremely leary about you using pipe dope on any threaded adapter from metal. Supposedly from what I've heard it's teflon only.
Also, is that the same one step PVC glue that the swimming pool guys use?