The other night I was dumping the black and got caught up chating with my in-laws who were camping in the next site. The next afternoon during a walk around I saw the tank open!
I checked the black level and saw it was 2/3 full????? Figured something was stuck on the wasis that measures the level. Ran the toilet and used the shower head to fill the tank. Dumped, and voila! Tank now empty. I hate it when I do sh*t like that.