On the passenger side of the coach, 3rd door back look for a "low point drain" decal.
look under the coach at that point and you will the termination of 3 water lines, 2 with caps on them.
the one I'm pointing at with the black tape wrapped around it is the fresh water tank drain. The large clear one is the overflow from the dress water tank. The other capped line can drain all of of your fresh water line.