Black water toilet plugged

You could put some water in it and rock the trailer back and forth so the water sloshes to help break up the plug if it is really bad. we had a Forest River that for some reason allowed the paper to plug up after just a couple uses. I poured water (clean) from a bucket held up high with the toilet valve held open to get some velocity. it took a couple bucket fulls, but it finally broke up and drained.

After that I had my wife and kid use more water.