Aquabelle....in my case (Post #27) I was referring to the antifreeze coolant side, which I refer to as the fresh water side (not seawater side). But maybe that is the wrong interpretation.
Jerry: I understood your post correctly...and to answer your specific question, no problem at all with flushing with regular tap water so long as you final-fill with anti-freeze-treated distilled/demineralised water.
rgds