Sewer gas issue

This week i had terrible sewer gas smell. First with tanks nearly empty and second with tanks about 1/3. It is 2016 winnebago 38Q. The washing machine dumps into black tank. I had one of those fan like things installed on my vent tube when having service as there was a special and they seemed like a good idea. Could this have caused the problem? I did a dumb thing-i was running dash air with recirculat butto pushed which pulled stink to cab. Once i took outside air it got better.

Finally, one week ago i really cleaned tanks well using build in cleaner. Any thoughts before i head for shop?