I have a 2005 Mandalay 40B and have owned since 20,000 miles, has 34,000 now. It has always had a bit of a sewer smell when driving. I do not run with vents open, both tanks have been bleached but o...
there are 'vacuum breaks " like what goes in near washer or dish washers in the home, on some MH .... time allows them to dry out and seep odor from the GRAY tank