AS you can see there are plenty of variations on the theme, but the consensus is to avoid ANY harsh chemicals, bad for your system and bad for the campground septic system, potentially bad for you too if you have a spill.
As a group we range from the super clean systems to the just get rid of the black water. Both seem to work for different people. The real key is to not let it dry out. As for the gauges, they either work or they don't. When they don't, even the most serious cleaning may not fix them for more than one or two tankfuls. We learned early on just how long we could go on the tanks under different conditions and made notes as to when they were dumped last - post-its in by the gauges.
I have been in the just get rid of the poo camp for 14 years in three different coaches and have never had odor problems or other difficulties with the holding tanks.
We use a macerator system which means we do not get the "rush" of water when dumping the tanks, just a steady flow as the motor grinds and pumps the effluent. WE have a need to reach a dump that is over 100 feet from the coach and slightly uphill when visiting family, otherwise I would not have spent the bucks. Having spent them I enjoy the small hose and general lack of exposure to the effluent.