Here is one that i have used before and it worked good. When i had my new roof put on i had the installer put on the sighon 360 roof vents. No smell at all and nothing but water in tanks. Hope this helps.
Another formula for cleaning your tanks came from another camper on this forum a while back. Seems to work very well for us. No odors at all. In a gallon plastic jug put together 8oz pine-sol, 8oz liquid fabric softener, 8oz household ammonia, and 8oz baking soda. Mix with a quart or so of water, then fill the gallon jug the rest of the way with more water. Mix, then pour about a cup down each drain (sink, lavatory, and whatever else you have), then pour the rest of the gallon into the toilet. Follow with 2-3 gal of water. If really dirty, add 20lb ice cubes and take a 1/2 hour ride and dump. I put this concoction in every time I dump, and never have any odors from any of my 3 tanks.