Often, a bad smell in the bathroom or kitchen is a problem that starts on your roof.
The diagnosis: Your rooftop vent pipes are too short. Most plumbing systems vent out through the roof. If the home faces north or south and its ridge line runs east and west, the sewer vent pipe sometimes emerges on the north-facing side of the home. Because the prevailing breezes in Arizona come from the south and southwest, they hit the south side of the roof and roll down the north side. If your vent is on the north side, this can create positive pressure in the vent—designed to release sewer gas into the air—forcing the gas back into the house.
The solution: Buy a five-foot section of corrugated high-density polyethylene pipe from the hardware store, and slip it over the vent pipe. That will make it tall enough to avoid the draft, and will send the gases far away from the house.
Nine times out of 10, this eliminates odor problems in the home and around the yard.