Disconnect the toilet fitting from the rear. The fitting is on the right rear and may take a pair of channel locks to loosen. Make sure you shut off the shore water and don't have the pump on b4 you do this. Also reLease the pressure on the line by opening the cold water faucet in the bath room. And press the pedal to let the remaining water pressure drain. Once the water stops flowing unscrew the fitting in the right rear of the toilet and have a small cup to catch he water.
Once disconnected you may need to run the water via the pump to remove the blockage. I used an old washer drain hose placed over the fitting that comes over the wall connected to an empty water jug. Even after flushing the line after winterized I have found fine plastic pieces in the screens.
If you don't have the tools or time to this while camping keep a jug of water in the bathroom you can flush by adding the water manually until you get home.
I just had this happen in nags head. I tried to pull the valve and couldn't get it t out next to the wall so I pulled the toilet (all 2 pounds) pulled the valve and cleaned it out. Flushes like a real toilet now. Think I am going to dump this one and get a porcelain one when I get home
2015 FR3 30DS