I like plastic fittings they work just fine. I have some of the schedule 80 grey plastic ones used on a seacock for splitting water to heat pump and a utility pump, bought them at Lowes. If say I managed to step on it and it broke, which it does not break, I could always turn off the seacock.
The schedule 80 black polypropylene fittings I think are better and tougher than schedule 80 PVC.
Got a 90* from Amazon cheap. I installed in the discharge line from head to the seacock. I pump out the waste into the water. My connection hose is that standard white PVC.
Examples here
Polypropylene Threaded Pipe Fittings Category | Polypropylene Pipe Fittings and Polypropylene Pipe Couplings. | U.S. Plastic Corp.