Well, I have done a bit more research on the tank monitor systems. The typical monitors are made by a company called KiB Electronics in where else... Elkhart, In.
The "sensors" for the tanks are nothing more than a bolt inside of a rubber grommet, wherein when the bolt is tightened, the grommet expands to seal the tank.
There are 4 such bolts in each tank. The bottom most bolt connected to ground, then the upper three bolts at approximately the 1/3, 2/3, and top levels of the tank.
These bolts are then connected to a "resistor ladder" network between the ground bolt and the three upper bolts. This allows a variable resistor of sorts, as the bolts under the current liquid level is shorted to the ground bolt, more or less.
I see several potential issues here.
First, water is actually an insulator. At least pure - distilled water is. What makes water conductive is the particulate matter found in tap water such as minerals; and for a holding tank, it's organic contents as well as any enzyme or other additives.
This means the conductivity of the water can vary significantly, which in effect, does change the resistance readings the resistor network provides. However, with only 4 data points (empty, 1/3, 2/3, full) in the monitor system, the tank reading is not all that accurate anyway, so this may mask any error associated with the variable fluid conductivity.
Secondly, and probably more important, the bolts protrude into the tank, which is I believe where most of the problems come from as tissue or other matter could potentially cling to the bolts, thereby creating a false reading.
The third issue I see is even an empty tank will be wet, which can affect the reading until the tank sides dry out, especially if it is wet/dirty water.
In my experience, the fresh water and grey water tanks in my coach do not generally give me as many problems as the water is cleaner, and perhaps not as affected by the particulate matter suspended in the liquid.
In contrast, the tank monitor system I had in my boat, which was very reliable, was an external sensor system, with no components to protrude in the tank. The sensors worked on the principle of capacitance, wherein the capacitive value between two vertical metallic strips changes in accordance to the fluid level inside of the tank.
The advantage of an external system is there are no components to foul, nor is the accuracy particularly affected by fluid contents. And there were 10 or more data points to the scale if I recall.
My first solution is to try and get a fresh water flush system installed, and especially locate it so that will spray water on the bolts used for the monitor sensors. If I can keep them clean, perhaps the tank monitor will not give false readings and I won't have to proceed further.
If that does not work, I am looking into the feasibility of adapting those sensors to the KiB monitor display, at least for the holding tank. I am very confident I can do it with ease, but my major hurdle is I would have to run a power wire to the sensor as they are active. As well, I am concerned about battery drain as the sensor and conversion circuit will take some power from the system.
Whether I can get the system to turn on when readings are taken - then shut off between readings to conserve power is probably going to be more of a challenge than interfacing the sensor.
I should contact the guy that did the videos and encourage him to do the experiments with 4 of the KiB bolts in the tank, and see how or if they foul.
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