I do not have an answer. However, I will be watching to see what folks may say. My motorhome has never had this issue until this past weekend. We had some low hanging tree branching run across the roof pretty good, and I later noticed the cap was not off slightly. I climbed up and snapped it back on, but have had the sewer smeel ever since. With the caps on as they were supposed to be, and freshly dumped and rinsed grey and black holding tanks, I am hoping that when we go to use our motorhome next weekend, that I do not have these odors. So, I am open to any feedback, as well.