Sounds like the condo assn needs to work on this -- a job for a Roto Rooter sort of company. Either the pipes have gunk along them, or tree roots are blocking paths and holding the smell, or . . . ??? Must be other things, I'm not aware of, lol.
A temporary fix: put down a box of baking soda and then add white vinegar. This will foam up, and help clear pipes of gunk.
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