Black tank smell in coach

What's Next? wrote:
I have had our coach for 7 years now and every once in a while while driving I get a really bad smell coming into the coach. It smells like the black tank is venting into the coach. The weird thing is it doest smell bad in the bathroom. I always flush out the tanks really well and add chemicals to the black and gray tanks. Any help is appreciated.

Use a lot of water and dump often and in which case, chemicals aren't needed. Like 4 days tops with two people. Most likely it's air down drafting through the vent pipe and in stubborn cases, it's often been found that the vent pipe was installed all the way to the bottom of the tank, rather than near the top. Some have installed electric exhaust fans on the roof, but not sure of the results.