The tank sensors are notorious for not being real accurate. I can dump ours until nothing comes out and the sensor can still show 1/3 full sometimes. The next time it might show empty. Just a thought, when you did your PDI did they have the water hooked up to test for leaks, etc? Maybe they forgot to empty the tank. And just so ya know, it's grey water, not Greg.
2020 Flagstaff Micro Lite 22FBS