Sewage? Or is my dog just farting?
“Periodically” is the key word.   Keep a log of what water usage (if any) you’re using when the offensive odors blossom and look for correlations.   Might want to keep a log of what you’re feeding the dog too.   (grin)  The source of odors may have nothing to do with your water usage.   A friend can tell the speed of the wind by fluttering of water in one of the toilets, when it is really windy a stink will fill the house.   He’s had the vent pipes (http://en.wikipedia.org/wiki/Drain-waste-vent_system) cleaned to no avail.  Another friend can tell when the neighbor gives their dogs baths, apparently the abundance of soap bubbles interfere with the vents.  (Too long for a comment.)