If the buildings vent stack is operating properly smells shouldn't be coming out of the drains, no matter how much they pour down it.
If the vent stack is clogged or insufficiently sized, air could be forced up through the traps, but you'd be smelling sewer gas too. It's a really rank smell you'd notice, so I think the polysytrene smell is probably coming in some other way.
I did home renovation work for like 8 months. Some of the people in the crew practically destroyed their bodies doing that work for 20+ years. One of the drywall guys would have to use his left hand to loosen his right's grip on the knife because it would get locked up. There was another guy that was maybe 45-55 that walked hunched over like a 90 year old man.
I actually liked the work compared to other jobs I'd had, but the "work through the pain" culture was so toxic. Everyone would act like working hurt was both mandatory and something to be admired.
It's fine to be proud of being a hard worker, but being proud of destroying your body for a boss that wouldn't give a shit if you died is sad.