We own a 2004 Coachmen 300QB (Mirada) and drain the fresh water tank using the control panel located in the rear storage. Our panel illustrates how to position each knob to FILL, USE, WINTERIZE and DRAIN the tank. The water drains from underneath onto the ground. The part you're looking at is where you siphon antifreeze into the holding tank to winterize. If you're planning to do it yourself, be sure you drain the excess water after blowing out the water lines. Otherwise, you may have a cracked drain pipe come spring (like we did).
Mike & Michele
2004 Coachmen 300QB