Keep cleaning and flushing until just water comes out. Take off all airators so they don't get plugged. And flush thru lines. I think those blotches coming out are what was in your tank and working them selves out. Can you get some ice cubes in tank and take it for a ride to agitate? After you think you got it all out couple extra times might not hurt. What a eye catching title Maybe residue in fresh water tank might be better. If you have a ice maker see if you can find a water shut off valve for it, you don't want that in there.
(To cheap to buy new)
1990 37 ft 5th wheel that hasn't moved since 1996 (our best home)
1997 33 ft trailer (winter home in much warmer climate)
2005 25 ft M/H (our "stand up B" for traveling)