Burl, I think that because there are short times that the opening to the tank is open during flush, and the fact that the chemicals are designed to break down the waste as well, are 2 reasons we need the chemicals. The only thing, AFAIK, regarding the vent pipe is if it's clogged.
Rodger, you are a nice person and moderator, but we are all talking about problems with our B+'s. I don't see how we are off topic, since our point of reference is the same, and in Burl's and my case, exact same models.