The vent is a hard line from the top that has an elbow to go straight down. It is clear up to the elbow. Not sure how to check or clear past that. But I think that is open. Great suggestion and I was hoping that was it.
I see with some looking that I fill the tank from the bottom. Maybe they are all like that. But that means that I cannot add bleach after there is any water in there, as it pushes back at ya and closes the check valve/backflow preventer. How do the rest of you add bleach for sanitising?
Thanks for the help thus far. We will figure it out eventually.