Like many other rv owners I use pool shock to clean my fresh water tank...about 2 tablespoons of dry powder to a full 30 gallon tank.
a bag of pool shock powder is a few dollars at the pools store or home depot
I'll leave this in the tank for a couple of days and let it slosh around while I go get the tire pressure checked ( costco) and get supplies...put a few miles on it.
I'll then run all the taps and move this through the systems.
after this I fully fill and flush the fresh water tank with city water.
works fine
http://rvbasics.com/techtips/sanitizing-your-rv-fresh-water-system.html
like "bleach" this is corrosive so handle with care- I do carry a plastic container with powder in the van, easier than carrying liquid bleach
mike