I have a new home (1.5 years old). Immediately upon moving in I started to notice intermittent smell. A sewer smell that starts in the basement utility room and lower bathroom and then spreads through out the house. The smell is almost always strongest first thing in the morning and most pronounced when it rains lightly over night or in the early morning.

First the basics:
* Septic Bed is in front of house. Above grade from the basement.
* Plumbing configuration has an injector tank in the basement services two bathrooms and a small kitchen area.
* House is large and tall. Vent stacks are at least 25-30 above the septic bed
* The utility room has a vent stack (services 2nd storey (2 bathrooms), Main floor (washing machine), basement (bath)
* All fixtures get used at least 1 per week
* Package of Septic system enzymes are being added to the septic tank on a monthly basis

When we first experienced the smell. We called the Plumber. He went to injection tank and sealed it with a silicone caulk and screwed the lid back down. The tank was not sealed.

However we had a re-occurrence. Plumber came back, replaced the wax ring on the basement toilet.

3rd occurrence, tracked to faulty air inlet value on laundry room sink (note: not part of vent stack mentioned above, this had one of those small inlet that pull air from the house when used). That was replaced.

The problem has continued. It was good all winter and now that the summer is here, the smell is at least 1 per week. As I said, the smell start in the lower basement corner. The room with the main sewer line, the injector pump and the vent stack for the lower bathroom. The bathroom has the second strongest smell (it is next to the utility room) then the kitchen (above).

I have a feeling it has to do with the air pressure outside and the fact that we have a heavy clay soil (Georgia). My theory is that when it rains the ground can't allow the "air" to escape from the septic bed and the gases build up over night, forcing the air back into the basement of the house where it escapes through some fault/fracture in the lines.

I think my next step is to have the vent line smoked or peppermint tested for leaks. Of course I'm not 100% it is the vent line. I know the room has the strongest smell. This is a rough diagram of the space

A - Sewer Line
B - Injector Tank
V - Vent stack


****************A**

* * B *

* * *

* Weak * *

* Smell * *

* (TV) * Strong *

* * Smell *

* * *

********** ***********

* *

* Utility Area Strong Smell *

* *

**********************V******

* *

* Medium Smell *

* (Bath) *

**************





Any suggestions? Thanks in advance.