I had a 07 Cardinal WB30LE and the handle by the wheel well (furthest towards the rear of the RV) was for the Galley/kitchen, the handle all of the way towards the front is for the black tank and the one in the middle was for the shower. I can't remember if the bathroom sink drained into the black tank or other grey tank. Perhaps someone with your model can verify. if you don't get an answer here, there is a Cardinal Owners Club forum.
2015 Rockwood 8329SS TT
2004 Chevy 2500HD D/A 4X4 CC SB
Andersen Weight Distribution hitch