This is interesting to me as I also have the same problem of an outside smell on occasion. And, after reading this post, yes, it does occur to me now I only smell it on cold days, and not every cold day. I also do not smell it during the summer months. I did finally decide it had to be coming from my vent stack and thought I shoudl go make it taller but now this post confirms that. And, my friend is going to install his septic system this Spring. It will be a seepage pit and it was suggested to him by the State of NM inspector that covers our area, as his lot is not large enough for a standard leach field. Thanks for the info! What a great post.