We've put water down the vent stack and it goes all the way through, we've smoke tested and smoke comes out the vent, we replaced an "s" with a p-trap on the laundry. We have no dry traps. What we do still have is sewer gas smell. It's not constant and is only noticed in the warmer months. Should I suspect a faulty (cracked, separated, etc.) vent stack? Time to break out the peppermint oil? Thanks!