Looking for fresh water drain

Trace the lines from the FW tank to where they exit through the floor. While I don't have a unit like yours, my drain would not drain either and last year I was forced to pump the FW tank dry (almost) with the on board pump. You don't need to drain it entirely dry, if a bit of water freezes in the bottom, no big deal, won't hurt anything, however, I found that I had a blockage in the drain line so I blew the line backwards with compressed air. Problem solved.