You were arguing with a person who has a great deal of time "In the Foxhole" both Lefty and I are aware that the sensor might be applied in the manner described, posting the "App Notes" is good education, however the situation isn't changed by your research. In the "Real World" app notes frrequently belong on the Loo.. better purpose for them there. Your solution would be inapropriate for 1. Potable Water (toxic contaminants), 2. Any media containing active halides
halogenures (Cl content < 50 ppm)
and this includes the florides like freon and both have high solution mobility. 3. Any petroleum based liquid (solvent). 4. There is a good reason that the Mfr suggests or specifies the device at some particular operating voltage (calibration) use at other lower voltages might be possible BUT are you ready to completely characterize the sensor at the new voltage? one side effect might well be compression or non linearity in the returned data. There is an old (when I was young)
Maxin that says... There is never enough time to do the job right and always time to do it over again" This is the reason why Lefty told you to buy the proper sensor rather than try to make a dry sensor work with a liquid. You stated thhat there would be a "Dry Tube" and Lefty mentioned that Air will compress but a liquid won't... so your returned data is anyones guess. BTW the link to the App Note is broken, I wonder why. Lefty has years of knowledge of what works and why. The advice is good and free as well so why not use it. 8 Volts is easy to do with a simple boost mode switcher and some light filtering 2 47uF caps and a 100 uHy choke should work well. My apparent anger isn't at all just my impatience with people who argue with answers that don't fit their own world model.
Good Luck in the Contest...
Bob