On my '07 WC the grey tank for the shower and bath rm sink is forward of the black tank then the galley sink grey tank is behind the black tank.
They All drain out the same big outlet and all have separate valves...allowing me to rinse the stinky slinky with both grey tanks if I want to.
'5picker'... has a good point that it may have been repaired.... or perhaps it was a Friday nearing 4:00pm when they installed the valves in your RV.
It is relatively an easy fix...if you can't live with it the way it is.
'07 WildCat 30 RLBS ~ West Coast Edition ~
Trail Air - Tri Glide Pin Box
2000 F350 DRW 7.3 Diesel Lariat 89k miles
Edge programmer, 4" SS exhaust turbo/back
Vancouver Island, B.C., Canada