I have the same problem, but when I had the basement wall off for something else, I disconnected the water line between the back-flow check valve and the black tank. I hooked up a hose to the easy flush fitting in the convenience center, and a length of hose from where I disconnected the PEX to outside of the basement. Then I turned on the water and it flowed OK through the check valve. So that means, it is plugged downstream from the check valve.
After a phone call to the easy flush guys, and finding out that there are no moving parts in the tank sprayer head, I have concluded that the sprayer head is clogged up with dried Poo. I have tried filling the tank completely full and letting it soak, opening the black valve and leaving the water turned on to the easy flush for hours on end.
There is still no joy in Mudville! (pun intended) I think that I will try to make a miniature Roto-Rooter out of wire and try to clear it up that way. If that doesn't work. that leaves me with taking down the belly and removing it from the tank to clean it out. I think I will leave that one for the dealer to do, as it is still under warranty.
