When we lived in the country, we had asked our LL when was the last time it ever was pumped out, he said, I dont remember maybe 20 years or more?
When we opened it up, peeeeeeee ewwwwwwwww, and all that buildup of solids was FULL and the septic tank was not that big. It was something like two men's armwide length and eight feet deep and it had plate size holes all around it on the walls. I have not seen those type of septic tanks but for whatever how long it was, it was FULL! So the solids has been pumped out and our water outtakes worked well since then. When we asked our septic guy, he said to get it pumped out every two to three years with a family of four, dishwasher and washers. The water is already out to the "fields" so there was NO liquid. Obviously it has been working well but it is unknown HOW long it was sitting there.
Anyway with the city and sewer guys, they said that Rid X is a waste of money. The septic should do its job without any "additives" into the tank.