2011 Mirada 35DS Tank Configuration

[BLGC]

We have just purchased this unit used and have had problems with the rear tank and odors in the rear bays on both sides. We are trying to figure out which items drain into each tank? its a rear full bath and 1/2 bath in front. The rear tank has a 4 inch only drain (black) the front has a 4 inch (black) and a 2 inch (grey). We know the rear tank had (stuff) left in it and was dry, so i used the sani flush several cycles and then to try and fill/flush it but when it got to the top the sink backed up? and the studdar valve under sink had water come out, yet shower was dry? so i assume the rear sink drains into the black tank, shower drains into the grey mid rv tank along with the kitchen sink and the 1/2 bath sink and the front 1/2 bath has its own black tank?. i have read about these B&B valves on the saniflush inlets? i have not seen these under my sinks just the studdar valve on a tall 2 inch pipe kind of a 1 way air valve to drain the sinks. besides this we love the unit so far...