Drain odours inside can suggest a completely dry trap, cracked air vent

https://canvas.pasadena.edu/eportfolios/4924~6653/home/common-plumbing-leaks-that-you-may-experience-in-your-home

Sewer odours inside can suggest a dry catch, broken air vent, or partial blockage; Geelong properties with large trees or older sewer lines might need CCTV evaluations to find invasions and avoid persisting scents.