[Nebster]

Why aren't the other drain lines serving as additional vents into the tank when the sucker is doing its thing? I would think there would be tons of redundant venting -- or at least there is in my coach, looking at the many independent lines plumbed into the top of my waste tank. What am I missing?

I mean, sure, the sucker truck guy has to have a little common sense and go easy on the vacuum so as to not overwhelm the system. But I suspect a collapse is a super rare event.

I'd hate to carry around a random intermediate sewage tank just to be able to get pumped out once in a while.