Hello: I’d like to know everything that’s in the water system, but as a start, put a spring loaded check valve on the recirc line and set it up for flushing.
Doing this means coming out of the tank port where the drain would be with a lined steel nipple, brass ball valve, brass nipple, brass “T”, out other end of “T” with brass nipple, ball valve and hose adapter. Coming out the center of the “T” should be brass nipple, spring check, brass nipple, ball valve, brass nipple to pump and on. Or you might want to put that last ball valve on the other side of the pump.
Yes, I know, a picture would be better 😉
This setup will allow you to flush out tank and piping separately and will keep yucky stuff on the bottom of the tank from getting into the plumbing in the first place.
Yours , Larry