When someone suggests using bleach, chlorine tablets, or another strong oxidizer on a waste tank, I'm sure that some suppliers sport an evil grin, knowing that it is the surest way to accelerate the sale of a replacement tank.... But don't do it. It will drastically shorten the life of an aluminum tank, and contrary to conventional thought, doesn't do 304SS any good either.
Simply keeping it clean with daily rinsing is enough for most. In more extreme situations, use a relatively inert (corrosion-wise) sewage deodorizer such as Odorcide or Hydrocide.