Tried them all and this is what I found to be even better than Happy Camper. And IMHO the 'only' one that actually works.
And it worked even in the incredible heat of a Florida summer where I had no hookups and full black tank between dumping.
Note the words 'powerful odor control' on the label.
There are two different types of this holding tank chems on the same shelf by the same company.
The one that states on the label.
"powerful odor control" and "breaks down waste" is the ONE to buy.
As far as your gray tank no need to use black tank treatment. Just pour a quart of any lemon cleaner into tank every other dump or so.
We must be willing to get rid of the life we've planned,
so as to have the life that is waiting for us.