Empty your HW tank, flush it with a tank flusher/your white hose stuck in the drain opening and let er rip, when finished doing that pour some bleach, maybe 1/2 cup into tank via the drain port, if you can get that much in, close drain port, fill the tank from your fresh water connection, open your taps until you can smell the bleach and then shut them off. Let it stand for maybe a day, if you can do that. Drain the tank and then refill and hopefully that takes care of the smell. I had the same problem, used bleach and so far no smell and we're into a month and a half of traveling using different campgrounds(knocking on my head). Good luck.