1.) Plumbing systems are designed to prevent odors from creeping into your home. P-traps hold water to keep fumes from sewer lines invading your home. If the water in the p-trap evaporates then the seal is broken and sewer gas can find it’s way in.
2.) What to do: run the water at each fixture. This will fill the p-trap with water and create a seal. This seal will keep out the bad smell. If that doesn’t work then give us a call at (518) 671-6009 for further inspection.