Put black tape over monitor/indicators and stop worrying about them
After a few camping trips you will get an idea on how long you can go before having to dump
(Instead of city water connection.fill fresh water tank and when it goes empty it's time)
Toilet 'burps'.....time to dump black tank
Sinks/Shower start to drain slower then usual .....time to dump grey tank
Water pump goes 'buurrrrrrrup'....should have added water already. Tank is empty
OR you can use the 'GEO Method'-----dish soap, water softening agent (Calgon)
OR you can use a digester product like Unique or any of the MANY sold for 'tank cleaning'
I don't pay much attention to cleaning tanks...that are holding tanks, get filled with waste, dumped and filled again.
So indicators get stuff on them and give faulty indications over and over again.
I have too much relaxing/camping to get done then get all OCD over those monitors