OK,
I’ll try and put this to bed. I did a search and the device I’m referring to in the above thread is known as a Black Tank Anti-Siphon Valve. Google defines it as a “specialized check valve that prevents wastewater from flowing back into the fresh water supply line”.
That stated, it is not an AAV (my mistake) so…..
To the OP, this “valve” did fail on our MLE but it’s not a big deal to replace (inexpensive) or remove and use a vacuum breaker at the point source. I say this because it was a very easy fix to remove the valve and replace it with a brass nipple which was available at a Home Depot (along with the vacuum breaker) close to where we were camping when it gave up the ghost.
Good luck with your MLE. I think you’ll find it was a good decision. Enjoy.