Drain odours inside can indicate a completely dry catch, broken air vent

https://www.pitchero.com/clubs/eyelsh/news/common-plumbing-leaks-that-you-may-experience-2923600.html

Sewer odours inside can show a completely dry catch, cracked vent, or partial clog; Geelong residential properties with big trees or older sewer lines may require CCTV inspections to find breaches and protect against repeating scents.