Our coaches should be similar, except for length.
Open the storage bay door opposite the wet bay. On our coach, that storage bay contains the batteries (rear section) and a storage area (front section). In the front section there is an access panel. It's 12 inches high and 18 inches wide. That's how I get to the valves.
You can remove the white panel in the wet bay, but probably you'll find the black water valve too far away to reach from that side.
It helps to be small-bodied to work through the access hatch.
Our coach was supposedly built with rod-operated valves. By the time we got it, it had cable-operated valves. I got so frustrated with them that I rebuilt the sewer piping. Now the drain valves are directly in front of me when I open the wet bay door. It was a lot f work, but well worth doing.
2008 Holiday Rambler Admiral 30PDD (Ford F-53 chassis)
2009 Honda Fit Sport