I’m so glad I found this thread! I have a Holiday Rambler Vesta 30F (virtually the exact same model as the Jamboree 30F). I asked my dealership about the fresh water drain and was told there was not one. I have looked everywhere. Based on your post, I guess I now know where to look. Stupid question - did you access this panel from inside your RV (under the bed) or from under the RV?