Tank chemicals fall into a few categories, Rid-Ex is not in any of them (It is not a chemical, it is a Biological and will be covered next "Chapter"
Preservatives, these often contain Formaldehyde and in some places if you are found to have them in your RV you may be ask to ... park elsewhere
Deodorants,, Really not all that effective.
Sensor Cleaners Same as the above but with a bit of table salt added.. Yes, that's all, just table salt, do nothing to clean the sensors I might add.
Next Chapter (Did I mention they are short)
Biologicals: This includes Rid-Ex, and other Waste Digesters.
The problem with these products is they are slow acting.. I do, occasionally, use one when I know it will be at least 2 weeks between dumps (And living alone, I normally dump at the end of each campground visit (2 weeks) in the summer and in the winter it is 1 week/2week/1week/2week pattern)
These may actually clean a sensor on rare occasions. These are the ONLY Tank additives I suggest and like I said then only if you can go 2 weeks or more between dumps.
Otherwise. Water, Just plain water.
STINK: First, I have found Gray water is way worse than Black.
Second: You may have seen the ads for the chemicals showing the stinky rig.. Well, I managed to be that rig one time.. Turns out I had left the gray valve open and sewer gases were backing up into the tanks.. Closed the valve and away went the stink. Like magic.
One other time we had that problem, This time in an office building... People were complaining about the stink in the men's room.
I poured a quart of water down each floor drain,, Stink was gone an hour later.