Originally Posted by kc5mhb
Don't forget you also have a sewer vent that exits the top of your trailer. When you flush and have your black water tank closed and fantastic fan on; it will do the same thing. I don't always run with the black water open but seeing the photo, I just might try that. So yeah, with the tank closed and fan running, when you flush, the fan will pull air back through the vent and up through the toilet. I just tell the kids to turn the fan off and then flush.
Never, leave the black open for any length of time, you could be in a world of hurt down the road.
Even dumping the black daily is not advisable, reason being you need that water/liquid to move solids and TP out of the tank, otherwise it can stick and solidify thus creating a wall or jamming your valve.
To each their own but I really don't see the purpose in leaving the grey(s)open.
If you use lots of water when flushing the black then the tanks will roughly, I say roughly fill at the same time, therefore dump them at the same time, black first, then grey(s).
Like I say to each their own and if the P trap works for you then great, after all your doing this for your not me.