In a year and a half of the pin falling out, I guess it was only a matter of time before it fell in..........
John - your trailer came with a bag of books and one of them is most likely the toilet manual, with a breakdown of parts. Call the manufacturer. I have had good luck dealing with Dometic directly in the past.
What is this flush valve that is frequently installed reversed?
Is it the tank rinse?
The vacuum break valve?
First I've heard the factory has a habit of installing them incorrectly, guess i need to check mine.
I think the flush valve is actually a backflow preventer. I have one behind the shower access panel in the bedroom. Could see how if it was installed backwards then you couldn't clean out the black tank. Its a cheap black plastic backflow device with a pretty low PSI rating. I run a regulator when I flush my black tank.