Barnacle Buster, Rydlime, CLR are all strong acid based water scale removing agents. Even though they say use them at 25% dilution, they will work fine at 10% but it will take longer.
So dump in a gallon of one of these into your empty fresh water tank followed by about 4 gallons of water. Drive around for a few minutes to mix it up. Then after say a half day of sitting start the fresh water pump and run it through all of your fixtures. Let it sit for another half a day and then flush it out thoroughly with lots of fresh water, at least 20 gallons through all fixtures time and time again to get it all out. Be sure to bypass the hot water heater if it is a tank type.
Virtually all of your fresh water system is made of plastic parts that will not be affected by acid except maybe the shower head and other fixtures. I would at least remove the shower head when you do this as it often has a valve with tight clearances. The other fixtures will probably be ok if left in place.