I just found there is a wealth of "how to" videos on YouTube. Some of the guys are pretty informative and give probable causes for certain symptoms. Search "vacuflush head repair". Lots of things you didn't know that you didn't know you didn't know. Ya know??? Ball valves and seals, duckbill valves, vacuum swicthes and pumps - bowl to tank.
I should have known. A few years ago, my washing machine's agitator stopped turning. I searched YouTube using the brand, model and symptom. Up comes a video showing what was broken, the part number and how to replace it. Less than ten dollars for the part and it was done in 20 minutes.