I assume blowing the system with air also takes care of this tank? I also ran the pump until empty and no water coming out
Not really, The internal diaphragm has air pressure on one side and water on the other. With no water pressure in the system the diaphragm will be pushed all the down thus removing the water from the water side. Basically with the water system drained of pressure the tank takes care of it's self.
Mike
Blowing things out gets some but not always all of the water out. Pumping pink stuff in through the pump fills the accumulator and then the rest of the lines.
Push the schraeder valve in to release the air. It will not drain unless you uncouple the pipe and turn it on end.