Interesting. Well, I would assume that the drains are somewhere near the water tank itself which should be in the rear somewhere; under one of the benches or possibly under the raised floor in the rear? Maybe the drains are in behind the access panel that is below the bathroom door.
Found them. The drains are on the drivers side, just outside the wheel wheel, between the wheel well. Drains are inside, under the driver side rear couch, and you need to remove the bottom cushion to access the drains, found under the rats nest if wires. Rear most drain is the fresh water tank, front 2 drains are plumbing system drains.