I believe the posters are referring to the GEO method.
Our friend swears by it.
My DH is stubborn to a fault. If I make the suggestion he doesn't act upon it. If he reads or watches a video, oh, yeah..let's do this.
Calgon has been hard to find here during this pandemic, but I scored a small bottle and put the suggested solution into our black tank.
We will be leaving ina few days and will dump before hooking up to site.
I may eat crow.
We never leave more than a gallon of water with our chemical. Our black tank sensors show 2/3 full even after dumpling.
Calgon water softener is what you use for GEO