I have been thinking of what to do as well with this.  I am going to use some of the things I use for brewing that are non toxic and no taste.  That way I fill it up with cleaner then flush then fill up with sanitizer and the nflush.  
 
 
I am interested to see what other ideas are out there and I am sure it will be the RV cleaner.  > Date: Thu, 3 Jul 2008 12:46:30 -0700> From: dhanson@GORGE.NET> Subject: Care and feeding of a Westie water tank?> To: vanagon@GERRY.VANAGON.COM> > Got to thinking about my Westie water tank. Recently, I decided I don't> use enough water to keep it fresh in there and carrying around what, 16> gallons?, is a bunch of extra weight..some 200+ lbs, so I drained it out. I> guess when I go camping I'll just fill it up, but leave it mostly empty for> weight reduction when not traveling..So, what does everyone do for keeping> the water tank from growing all kinds of bad stuff inside if you aren't> cycling through water all the time? RV tank treatment? Very dilute bleach> solution?..Suggestions?> I know the bicycle water bottles I use, essentially the same material, get> pretty funky inside after just a few days if you leave them on the bike with> the top on..> Don Hanson