There are many mysteries that make life more fun and interesting. The surprise of a full holding tank is NOT one of them.
All the tanks on Q are made of aluminum (like everything else) so unlike plastic tanks… their contents and volume remain a mystery… until they are empty… or full… unless you find a solution. We found Gobius.
Gobius uses externally mounted ultrasonic sensors to periodically test the level of the tank. It is not an exact measurement… but an excellent guide that warns us when we are getting full.
Q was delivered with an electric macerator toilet that uses fresh water to flush. We were going to change this to salt water… but apparently maintenance is significantly reduced with fresh water… and toilet maintenance is IMHO to be avoided at all costs. We just needed to reduce the amount of water used for each flush. That is what the manual IN and OUT buttons are for. We use JUST enough water to do the job.