HELP! Black tank Clogged

I had trouble with a slow draining black tank a few years back. We were at a Nascar race at Michigan International Speedway and decided to have the pumper service truck clean out our tanks. The guy working the truck started to have some trouble and turned off the pumper and disconnected the hose. He'd sucked the cut-out from when they put the connections into the black tank in at the factory. It had jammed the flow. He told me you'd be surprised how many times he had run into this problem.