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Try some Extreme Cleaner made by Happy Camper. That will clean them up like new! I think their line of chemicals is superior to any other on the market and less expensive. I am attaching a link to their website in case your local dealer doesn't have them. Try about 10 gallons of water with that and a couple of bags of ice cubes that you put down the toilet. Drive around so that is sloshes around. It should clean them up good. You can't usually do ice in the gray tanks, but they don't get "stuff" on them as much! Hope this proves helpful here. Please get back to me if you need more later as all follow ups are included in our fee. http://www.5starhappycamper.com/
Did you have a chance to use some of this product? Please let me know what you think of it..............thanks!