RE: Fresh water contamination.
If the antifreeze is propylene glycol it is no big deal, if it is ethylene glycol a good flush with clean water will remove it. Don't contaminate the system with soaps or solvents,if you do that you WILL have a problem.
Adding soap or other stuff to the mix will only make it very difficult to clean the system. Just drain as much as possible from the potable water tank and refill with clean water, run the system to clear the lines to each outlet. Either drain and flush again or just keep the hose flowing into the tank(s) and out the faucets to flush.