I think that is what it is called--it is right below the master cylinder. It has a bleeder on the top of it. I am about to flush the entire braking system with new fluid and I am wondering if I should bleed the isolation/dump/proportion valve first before I do the wheels. I am flushing the system because I have new brakes all the way around including calipers, pads, drums and shoes. Any help is appreciated

 

Thats actually a proportioning valve. It should have a pin in the front and back (under a cap) that you need to push in, one at a time while bleeding from the master for the first time.
Dump valves and isolators are only on later ABS cars and part of the ABS modulator/motor.