Thanks SO SO much for all the help!!
The info here gave me enough confidence to remove all the screws from the flange and wiggle the base & down tube. The tube came out of the black tank's receptacle rather easily, with just a wiggle and a twist. Didn't see any type of gasket at all, it was just a tight fit and was not glued. Awesome!!
I want to keep all of these pieces and parts, never know, we might want to sell it some day & the buyers might want a regular toilet. So I'm going to go to Lowes and get a short piece of pipe the same size and cap/plug, put that in and the deed is done, Wup Wup!!
Thanks again everyone!!