Check your thermostat and ensure that the FAN switch is set to AUTO not ON.
In the Auto position the fan will only run when heat or cooling is requested.
I looked up your floorplan, you only have one toilet, having more then one blackwater tank would be, unusual and unlikely.
Having your #2 grey tank connected only to the clothswasher option is equally unlikely. Most likely the #2 is connected to the clothswasher and bathroom.
If you do have four holding tanks, the fourth -might- be the clothswasher (or sink/shower)
2008 F350SD V10 with an 2012 Arctic Fox 29-5E
When someone tells you to buy the same rig they own, listen, they might be right. When they tell you to buy a different rig then they own, really pay attention, they probably know something you don't.