In the apartment complex where I work, one of the apartments has a very bad rotting smell coming from the bathroom sink. I have tried chemicals and had lines water jetted with 180 psi. Checked vents and they are clear. Drains are clear and not plugged. Apartment complex is only 3 years old and the smell has been going on for about 4 months off and on. No other apartments smell. What can I do? I'm at my wit's end over this! Desparate; please help me!