Sewage system 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

Drain odours inside can suggest a dry catch, split air vent, or partial blockage; Geelong residential or commercial properties with large trees or older drain lines might need CCTV assessments to locate invasions and stop repeating smells.