I had the same problem this morning. The connection in the ground wasn't too much uphill but enough I couldn't just dump. I had to lift the sewer hose next to my trailer and lift it up along the hose all the way to the other end to force the stuff into the ground connection (kind of picked it up every foot or so). I had to do that 3 or 4 times for both my black and grey tanks. It was a PIA but I think they pretty much emptied. Next time I go camping, I'll make sure I can dump normally.
Depending on how much uphill it is, you can try what I did above or if you're just camping, maybe you can find a dump station somewhere on your way home. If you're staying awhile, I would probably ask for a different site if possible.
2015 F150 XLT Sport 4WD 3.5L EB
2014 Freedom Express 246RKS