I wouldn't worry too much about it though. I put it firmly in the possible but extremely unlikely category. I've seen other papers talking about the possibly of it spreading through apartment buildings though plumbing and air vents, and also spreading via shared spaces like hallways and elevators.
In the end, it's all a numbers game. If enough of the virus wafts your way and your immune system can't deal with it before it gets a foothold and spreads you'll get infected. If you've got a hole in the wall between you and your neighbor and your neighbor is sick and their virus is shedding like a stressed cat you might get sick too. We've also got plenty of cases where someone is living in the same household as someone infected and they don't get sick. It's really just down to the amount of exposure/viral load, and the immune system of the person exposed.
Yup, that's the research I was thinking of. Note that the transmission did occur, admittedly at a fairly low level.
China is full of buildings with many, many residents and far from airtight. Many buildings over there also do not use p-traps. SARS has been documented to spread through the sewer stack this way, Omicron spreads *far* better than SARS.
No, it's that walls aren't normally airtight. All the documented cases involved situations where there was behind-the-scenes holes (utility accesses etc) even though there was nothing on the surface.
Source?