Seems you are not getting much response here.
I am not familiar with your rig, but must be someone out there with an answer?
Generally (my experience) the drain is very close to the tank. Although I did have one that had the drain under the kitchen sink, mid coach, with the tank in the back. If nothing else you should be able look under the coach and trace back the water lines that come through the floor.
Good luck, wish I had a better answer.
Greg and Karen, the pups Bailey and Lily (St. Bernard mix and Beagle mix) and Lola (the attack cat)