We had a nasty rotten egg odor coming from our hot water tank. I did some research and between all the advice I found I devised my own method that worked. Pulled out the drain plug and cleaned it thoroughly. Got our pump up garden sprayer and put in a mixture of 1 part vinegar to 2 parts water. Inserted the plastic spray wand and squirted in all directions. I also removed the nozzle tip so the liquid sprayed more to the sides, rather than straight ahead. While spraying the liquid will run out the drain where the sprayer is inserted, so you'll get flowing out. After using about a gallon of the liquid I let it set for an hour or so then got the hose with a
RV water tank cleaning wand. This did remove the vinegar odor and reached up and all the tank. You will probably get wet!
And that's it! Replace the plug turn the bypass to open to the heater, run some through and you should be good to go. Or at least we were.
Hope this helps.