Oder in Bathrooms after rain...

Help!!!!!!!!!!!

I have a peice of rental property, it is a two story brick on a slab with cast iron drain and copper supply. It's on a septic tank which is about 30 feet from teh structure which is about 60 years old. My down stairs tennant as complained for years about an horrible oder (she discribes it as smelling like a latrine) that occurs in her bathroom every tiem it rains. I have had the tank pumped and done everything I know to do to get rid of it...I've found nothing wrong. Well, today my upstairs tennant told me the same thing (this is the first time it has happened to her)....the oder seems to be comming from her shower drain, but I don't understand how that can be...the trap is full of water. I have no sense of smell so I can't tell.

If anyone could shed some light on this I would really appreciate it!

Most odors inside of a home are coming from the toilet sealing to the flange with the use of a wax ring---I would lift the commodes (again if you have already done this) and check that the flanges are setting atop the finished floor and are secure, if they are the cast iron type flanges then seal them with a horned wax ring.
When it rains the rain water is entering the septic tank and that back pressure is pushing that foul air up into the structure--normally your roof vents would dissapate that air, but maybe you have a vent issue which is magnifying the effects of a loose drain connection problem.
Also you could have a smoke test performed on the home--normally when we do these we require an outside cleanout access, although lifting the lid of the tank and using the inlet pipe would also work

Russ....

Thank you for taking the time and effort to respond. I am sure the closet flanges are C.I. The tolets sit on a ceramic tile floor. Wouldn't the wax ring being bad cause the tolet to leak around the base when flushed? Hmmmm...I suppose unless the line were backed up it would not. I have not had the tolets off since the were set after the cermic tile was put in......probably 40 years ago. I guess it wouldn't hurt to replace them even if thats not the problem. Thanks again for your response.....at least I have a direction to go... : )

Chris