WOW! I would have thought the spinner small enough to make it out of a 2" sewer opening.
You know what I suspect? The Pyramid of Poo
A lot of RV owners do not know how to properly use a black tank. The biggest sin is not enough water. In fact I have seen folks hook up their RV and then proceed to open not only the gray valve but the black one as well
Depending on the mood, I will usually offer some friendly advice
Anyway, I am willing to bet that was your real culprit and your repeated dumps finally dislodged the pyramid 'O Poo
You might want to get some SEA-Zyme (or some use RV RidX), fill your tank with water, and let the enzyme/bacteria colony munch away at whatever is left in your black tank -- might not be a bad idea to do that to your gray tank as well - stuff washed down the sink and shower can cause a build up in the gray tank as well.