OK,
The fresh water tank drain is a small valve located under the curbside access panel in the rear of the camper. There is a "porthole" cover near the cold air return vent that you can use to get to it, but, if this is your first time I suggest getting to it via that access panel. Usually it is hidden under the duct work but it will be there. Once you find it and turn the knob on the valve to be inline with the blue pipe that it attached to, you should see water drain out of a small tube under the camper. Once it has finished draining don't forget to move that valve knob back to its original position that is cross-wise of the blue pipe.
Bill