How Much Calgon ?

Wow, never even heard of this and we haven't put anything in our tank since we started in the late 90's and current MH we've had 15+ years, and never had a problem with black and/or grey tanks and gauges all have worked fine. All we've done is when thoroughly black rinsing, when closed valves, added about 1/10th tank of fresh water, and off we go. We always flush with plenty of water for the most part unless long term boon docking somewhere, and then we will always top up the black and grey tanks before dumping with fresh water about a half/one hours drive before we dump typically to slosh around.

Now I'm wondering if we should have been putting this Calgon thing in the tanks all along???? What is the premise to do this if you don't mind me asking?