I use yeast and peroxide in my holding tanks to clean them out while going down the road and while it is filling up when camping. It gets rid of solids and smells in tanks. You don’t have to wonder if the black tank emptied out all of it’s contents. If you want to completely clean out your black water tank, with tank empty, add 4 ounces of yeast, 10 ounces of peroxide and 1 gallon of water. As you are going down the road it is sloshing all over the tank and cleaning it good.
[copied from post on FMCA]