It would help if you told us which model of RV you have. Yes, most of the units have two grey tanks. If you have a rear bathroom, you may have a second black tank. Looks the the handle is in the open position under the pass through storage. Did you try closing it, and see what happens on the rinse cycle? I would suspect that the washer would drain into a grey, not black tank.
As eightydo said, my second grey tank release is to the right of the drain outlet. It's a pain to get to with the slide out. We have a Voltage V 3105.
2013 V 3105
2016 F350 King Ranch CC 6.7 diesel dually