So I figured out my issue.
I opened the bottom so I could see the tank and I very carefully filled up the black tank until it was full full (using an endoscopic camera). What I found is that the seam of the tank at the top where there top is glued or heat welded to the bottom part of the tank is leaking ever so slightly. Thinking about what occurred, I believe that I let the tank get too full and it froze/expanded and separated the seam a bit. The leak is very small so I am going to try a repair with some West Marine G/flex epoxy. I did a bunch of research of all the products people have used and it seems this one has done really well for others. The other thing I can do is monitor the tank a little bit better and not let it get filled to the point where it would leak (although if it were full while driving I assume w/sloshing it may still leak if I did not repair it.)
If this does not work I will replace the tank next spring completely when I have more time. Right now I am drying out the tank so that I can repair it this coming weekend.
I appreciate everyone's feedback, it was very helpful and gave me some things to look at while I was still perplexed.