First, I'm not sure that this is what's happening but I suspect this is the problem. On occasion my wife and I find cockroaches in our house. This isn't very frequent (I'll find one once every few months) and we also have an exterminator who comes and sprays once every month.
However these random cockroaches tend to always be found near or in our bathrooms and, to my recollection, we've never found one in our kitchen or dining room - places where vermin could most certainly find food.
I've heard that if you lose water on your sewer line, vermin can come in through the sewers. Is this true? If so, what can I do about it? I also suspect that this may be happening because there have been a few cases where on the back end of our house (near a spare bathroom that is infrequently used) we will get a sewage smell. The smell is quite rare, and we've checked for leaks around the toilet, yet we can't find any problem with the toilet itself.
Are we losing pressure on the sewage line, which is suctioning the water from the toilet bowl and allowing vermin into our home?
If this is the case, this is super-nasty. Please advise.