I have a home for sale that's been vacant for 2 months. The first month there was intermittent activity there and water was run on and off. For the past month no or very minimal water has been run. 2 weeks ago tomorrow I had the dye test done which passed. Today someone looked at it and smelled sewage. I went over and I personally didn't notice it in the house (although they said they did). I ran water in all the drains, poured water down basement drain as well as added some bleach. After doing this when I went outside to leave I got a whiff of it (didn't notice it when I arrived though...only after i had run water). My outdoor sewage pipe(?) is near my driveway and that's the area I smelled it. Can the home being vacant and no water having been run for a month be the cause of the smell OUTSIDE, or does that only apply to inside odor? We also just had a cold spell (single digits at night) and today it was in the 50's...could that be a factor s well?

the underground sewer pipe has a smell in it ALL the time whether you use water or not.
a trap could have evaporated enough water to make a smell inside the house.
also a vent on the roof could smell.