First of all, be sure that there is no water leakage in the hidden (utility) part of your storage compartment. These flushers have a plastic atmospheric breaker check valve that are notorious for breaking (usually attributed to high water pressure) and dumping water all over the stuff in the storage compartment (like my $250 Progressive Converter/Charger).
If all is dry, and you are ready to go crawling back into the utility area the best idea/test I can think of is to disconnect the water line from the spray head on the tank and see if it runs water when an assistant turns on the black tank washer for you. See this instruction sheet from B&B molders, Page 3, box #6 to see how it is plumbed. I don't know if Heartland uses the "Spin Weld" or "ABS" sprayer, but you should be able to unscrew the line from the check valve to test the rest of the system (minus the sprayer head).
In all my years on the forum, I don't think I have ever heard of anyone having the system clogged up: on the other hand I have heard of water leakage disasters from the check valve all too frequently.
BTW, your rig is about the same vintage as mine. The black tank flusher check valve is up in the wall behind the toilet (viewed with you sitting on it) . There is some plumbing code that says it has to be higher than the highest drain, which they consider to be the bathroom sink. Later on they moved it to where you could access it from the round screw-off panel in the shower.
