Come on get real. I was a supervisor in a school cafeteria with the same problem, and all you have to do is pore hot water down the drains every once in a while, because when they dry out there is going to be that smell. Any plumber would have known to do that. Because you could only know where the smell is comming from. And people are going to spend thousands of dollars to fix a problem and all you have to do is pour water down the drain.