We've only had our Scamp 16 for a year so far, but have used the fresh water tank on probably a half dozen occasions. I usually drain the tank nearly completely when leaving the campground (I just drain it at the dump station). I fancy that leaving a bit (just a gallon or so by guesstimate) sloshing around on the drive home might be doing some good. Then when we get home I drain the rest and let it sit. A day or two b/f a next trip I'll run a gallon or two from the house to let it ride to the campground, and drain it before filling with fresh water at the campground. I've sanitized it only once so far (this spring, after draining anti-freeze and flushing thoroughly with fresh water). I used a very mild solution of bleach to water, letting it sit in a full tank, then running it through all the faucets, then flushing it all again with fresh water. I've read that bleach isn't really great on some of the fittings or valves or such, so I tend to be sparing of it. This "system" seems to have worked so far for us. Haven't noticed any unpleasant odors and certainly haven't gotten sick (so far).