I uploaded 3 photos of what I have to work with. The opening in where the drawer would be is where I have to crawl partially in to just to get to the stuff on the floor. There is no other access and it is quite difficult to maneuver in there with just one hand. The fresh water tank is on the left of the drawer opening. In the center of the other two pictures is a chrome knob (hard to see) - if you follow the blue hose with the black plastic attachment from the tank about 6" the chrome knob is in the middle. It's currently in the "closed" position. I don't think I could attach something flexible to it and still be able to access it without having to take out the drawer. I still don't know what's under all the foam and I'm afraid to root around in there with all the wiring in the middle of it. Presumably at the end of that chrome knob is more blue hose that goes into the outside drain hole in the coach.
As for the 12v switch - good idea, I'm just afraid I won't be able to maneuver around in there to be able to install it properly. I appreciate both comments and will continue to study what's there.......