On our 3006wk the Galley Tank, ( not sure what it's called, the one up front), is only for the outside kitchen sink, (proved that while camping). I assumed the same, that the gray water tanks are split 45/45 but not 100% sure. I was searching the forum too, to see if anyone did any "internal" plumbing to connect them together and didn't find anything.
2016 Windjammer 3006WK
2010 Dodge Ram 2500, 4x4, Diesel, Front Hitch, Air Lift 5000 Rear Air Bags.
Equalizer E4 1.4k/14k WD Hitch.
TST 507 TPMS
Furrion FOS48TA Observation Camera
Garmin RV-760 GPS