HI Mike,
I agree with what Ponti says in that they use Passive Stack Ventilation @ PW, and so do we here in the UK - in its UK Building Regs. What can be done however, if the "pong" is too bad in the bathroom, is to fit a fan to discharge into the stack, which will accelerate ventilation - please bear in mind however that it would need to be used frequently (to ventilate) as your in effect blocking the stack.
Harry S