Depending on how often you use the washer/dryer will determine whether the P-trap dries out. If you're not going to use it for awhile, a half teaspoon of mineral oil down the p-trap will keep it from smelling. Once the p-trap empties, it allows the sewer gas to come into the coach. You shouldn't have to pull the W/D to access it. Look behind the W/D and you'll see the tube. Try pouring a cup of water down there first. If your problem doesn't go away, then look for other more difficult issues. Start with the easy stuff first....Dennis