Inspected a small old one bathroom house today. The drain lines were 100% re-plumbed professionally. The plumber did not install a plumbing stack vent but instead used an AAV only.
The question is, what is the down side of not having a vent, only an intake?
The plumbing fixtures worked fine and no signs of the traps getting siphoned.
Can there be a build-up of explosive gasses?
Will the gasses bubble up out of the toilet?
Is this the set-up for an urban legend where the person blows up while smoking on the toilet?