Your plumbing system is designed to block out these sewer odors by way of the P-traps that are attached to each fixture. These traps contain water which seals out the smell, however, if the water evaporates then the odors are allowed into the home. To solve this issue take a bucket full of water and pour it into each of the drains you are experiencing an odor through. This should block out and prevent the odor. If it is a shower or sink you do not use often you may want to make this a part of your regular cleaning routine to prevent any future occurrences.