This is what we have used for over 10 years and it works great.
get a empty plastic gallon jug and add the following. Recipe
1 Cup of Pine Sol
1 Cup of houshold Ammonia
1 Cup of Fabric Softner. (snuggle or any other brand)
8 oz of Arm and Hammer Baking Soda.
Put it all in Empty Gallon Jug and add water to fill Jug.
Shake well and add one cup to each empty tank pour some down each drain. as tanks get half full add another cup. It stops Odors, Lubricates and cleans tanks and valves.
It works great for us and we have never had any smell or stink even when dry camping for two weeks in Death Valley when it was hot. That should take care of the problem.
2006 Four Winds Hurricane 31D, Steer Safe, CHF, 50 Amp Conversion, 3000 Watt Inverter, Toad is a 2007 Jeep Liberty Sport. Blue Ox Aladdin Tow Bar, Apollo Braking System