Thanks for all of the replies. Here is what I have done. I have checked all of the vents including the one under the vanity sink.
I have thoroughly cleaned the tank with a wand.
I live in my trailer so I am connected to a septic tank. I keep the grey water tank valves open but close the black water tank valve. I understand that it is good to keep water in that tank so it will not dry out.
I put a tank order product in the toilet everytime after I empty the tank.
Everything is fine for about two weeks and then an order starts coming from behind the toilet. I have pinpointed it there.
I am thinking about changing out the toilet flange seal.