I traced an odor to a nasty smelly hose a few years ago. Before changing it I tried a trick that (may) have come from Peggie Hall. I cut a roll of Stretch Tight food wrapper to get a 3" wide roll and wrapped about 5-6 layers over the hose. Stretch it tight and tie-wrap the end when done. So far so good. The only problem is that to do this you need access to the hose.