plumbing question - PEX fittings; brass vs plastic

pnichols wrote:
Speaking of RV water fittings, what are those white and black fittings for RV water pumps where one side screws onto the pump's inlets/outlets and the other side is push-on for the plastic hose coming from the freshwater tank?

One of those on the flexible plastic fresh water line feeding our RV's water pump broke and I haven't been able to find that plastic adapter/coupler anywhere.