If my Bounder is the same as your Discovery the drain will be in the 3rd or 4th compartment on the curb side . You will see the plastic ball valve over the covering of the frame rails . It's a long reach or you may have to crawl in just a bit . Make sure you
turn it the correct direction as the valves have a tendency to be sticky or stiff and the handle may break. My handle was red and yours may be also.
08 Diesel Bounder 38V