Hello: I have a slightly different take on this one. The plastic threaded goodie is in place of the usual lined steel nipple. You’ll probably want to use a basin wrench to remove the plastic goodie and then you will have the normal 3/4″ female threads at the tank.
Put a ball valve on a 3/4″ plastic lined steel nipple and put that in. Add the hose adapter to the outboard end of the valve. This is far stronger than using the plastic piece which could easily snap off should somebody bump the valve down the road 😕