Mystery solved on my black tank flush. Kind of embarrassed to admit this. I had hooked up the hose 2 different times at my RV storage place and did not have any luck. I was getting a lot of water leaking around the connection where I screwed the hose on. I assumed that there was something blocked in my system and causing the water to spray out coupled with the fact that the hose did not really seem to screw all the way in (should have been my first clue).
Brought the rig to the house and proceeded to take things apart. Called Forest River and they said my check valve was behind the circular access port in the shower. Looked there and did not see anything. I then spent an hour or more searching and going through the painful process of removing the exterior panel the surrounds the hot water heater (the back of my black tank is located there and I assumed the black water sprayer entered the tank there - which by the way is correct). Once I located where the sprayer entered the tank I noticed that the hose went up inside of the wall. Seemed a little odd. To make a long story a little shorter, I have a 2011 Georgetown 350 and to the right of my refrigerator is a small pantry with 3 or 4 drawers at the bottom. Pull the top 2 drawers out (have to release the clips to get the drawers to pull out). Look back in there through the openings for the drawers and there is extra space way back in there and that is where the check valve is located. Mine was clear so I could see all of the springs, etc. Decided to hook up the water with my garden hose at home to see if the valve worked. Hooked it up and it worked perfectly. I determined that the end of the garden hose at my RV storage lot is messed up and actually was not allowing me to put enough pressure into the system to activate the valve (remember it was leaking around the garden hose end).
The downside to this story is that I probably wasted 1.5 - 2 hours trying to solve a problem that at the end of the day did not exist.
Oh well, at least I know where the check valve is located in this particular unit and others will as well after reading this.