air in toilet

I have read many times over the years ago a vent pipe dropping down into the black tank. This leads me to think that the vent pipe just fits through a hole in the top of the tank and can slide up or down if it comes loose at the roof line. I find it hard to believe that this pipe would be that loose and not sealed at the tank. This couldn't possibly pass any type of public health laws or whatever laws apply to holding tank sealing. What am I missing here?

I'm thinking the OP has a poop pyramid which is causing his issues.