Sewer gas smell - new home

We have a new home and we don't live there full time. We have two levels with a bath and laundry room on each level and a powder room at the mid/entry level.
We are getting a strong sewer gas smell in the lower level. We have run water through the drains in case there is a dry p-trap, but this has not seemed to help the problem. There is one main vent in the roof. Help!

Possibly a leaking wax ring to a toilet may be to blame.

A smoke test of your drain system will most likely divulge where your sewer gas is coming from.

How do we smoke test our drain system?
Thanks.

Leaf blower

3 or 6 minute smoke bomb from your local plumbing supply


Wire the bomb to hang down into the cleanout, blow air into the cleanout OUTSIDE of your home towards the house. Have a few people at different spots in your home.

When the presence of smoke shows up....you'll find the source of that smell. Otherwise it's a guessing game where it originates.