RE: Gauges that work and gauges that don't…
Apples and oranges. Speaking as a mechanical engineer, any mechanical gauge (like your automobile's fuel gauge) relies upon measuring a fluid with a consistent specific gravity, like clean water or gasoline, with no debris in the tank. If you measure a fluid with suspended solids (like effluent in a blackwater tank), or a varying specific gravity (like soapy water in a graywater tank) then a mechanical gauge is just as likely to give a false reading or quit working altogether.
Electronic gauges are still evolving. Inside-the-tank gauges like your Catcon Micropulse are still subject to problems caused by the tank's contents, but lacking any moving parts, they are less vulnerable to damage and wear-&-tear than a mechanical gauge.
There's a good reason why the boating and RV industries are moving to outside-the-tank sensors like the ones on my Interstate's tanks. Whether they're the best in the long term remains to be seen, but at least the industry perception is that right now, they're more reliable and easier to work on when something does go wrong than either mechanical or inside-the-tank electronic gauges. Safer, too. Because you don't have to drill holes in the tank to mount them, you aren't exposed to the tank's contents and you don't create potential leaks; that's one reason why the same sensors can be used on my Interstate to monitor propane tank levels along with the fresh- gray- and black-water tank levels.
If it was up to me, I'd replace the existing Catcon Micropulse sensors in your trailer with drain plugs screwed into the same holes, and install an all-new external sensor system. But it's not up to me, and my advice is like any advice; use, ignore, or mock as you see fit.
Engineering: Finding complex solutions to simple problems you didn't even know you had.