Sewage gas smell in my restaurant

[Todd Webb]

I have a strong intermittent sewage gas smell coming into my bathroom of my restaurant. I have no floor drains, i am getting no backup, just smell. I had a smoke test performed and found leaks in both of my vents. one in the kitchen dishwashing area and one in the bathroom. Both vents were replaced and smoke test following showed no leaks. Smell is now stronger than before . I have spent thousands of dollars and have had 8 different plumbers out that cannot solve the problem. Any Ideas?