Congratulations on your new home. Don't be concerned about not having the Forrest River owner's manual. It seems they print a single version for all their models of motorhomes. It is so generic as to be useless. You would want to have the individual manuals for the various appliances and systems from the suppliers to Forrest River. You should also get the chassis owner's manual. Some can be found on the internet using Google, other may be available from people here on the forum.
A 2009 sales brochure would have the specifications for your model. Here is a link courtesy of forum member cfsoistman: Georgetown Brochures
As for the grey and black tank valves, that is pretty easy: The black will usually be the bigger diameter pipe and valve. They grey will be smaller in size. On a previous van camper I owned, the two valves were close enough together to mix up, so I put some black paint on the valve handle for the black tank, and left the grey tank valve handle unpainted (the metal color was close enough to grey).
As for the back-up camera, there could be several reasons for it not working. I would start with the simple ones, like trying the different input buttons on the monitor and checking to see that the video cable is plugged in completely on the back of the monitor.