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Moved into a new apartment.
Two new bathrooms.
Bathroom 1 that gets used all the time is fine.

Bathroom 2 rarely get used, suffers from a “stale or foul” smell I can’t properly described. Similar scents can be found in old public bathrooms. Maybe it’s from a lack of airflow.
Note in Bathroom 2, I recently had the ventilation fan serviced, the shower has not been used, and some caulking around the toilet is missing.
Can the lack in caulking result in unwanted fouling?

Any ideas on how I can pinpoint the source and have it properly addressed?