when you fill the trailer do you remove the plug from the filler vent?
At the beginning no. I did not realize it was a plug. I could hear the air comming out though (and I was afraid to break it).
Then I took the filler apart and tried again to top the tank, with plug remove. No change.
I used an air tank, but got same result by just blowing into vent line: at some point, water squirted out through filler. I know for a fact that the tank is about 3/4 full.
It looks like at some point, the vent line is bellow the water line. ???? How is that possible?
I have just bought a new vent tube and I will try to replace it. You never know.