Originally Posted by norty1
All your drains inside have traps and vents already.
I think he is having the issues with the stack vents that are under some of our cabinets on the sink drains. Since they don't run to the roof and with the windows closed it's one of the paths of least resistance for air to come back in. There are only little rubber flappers inside those and supposedly go one way but those fans can draw some air volume.
I would agree with the P-trap on the sewer hose to keep the gasses out of your grey tank. It does help a lot.