To answer your question, your best bet would be to get a
FLUSH KING that will allow you to direct a spray of water back up into the tank with a regular garden hose......that is, if the clog in the black tank is at the opening of the tank.
You didn't mention if the tank was full? It sounds like it is either empty or clogged.
I don't know how much experience you have with black tanks and the proper use of them along with the macerator. As long as the macerator can suck liquids from the black tank, it will do so. If no water, then it will not suck out the solids. So make sure you have plenty of water in the tank to begin with.
If the problem lies in the macerator, the problem is that one or more of the vanes on the impeller (not the steel blades) has broken off and it can no long create a suction. The macerator will need to be disassemble, cleaned and a new impeller installed.
Good luck
Ron