Where is fresh water tank drain?

I had this same problem last week. Ended up simply tracing the lines coming from the tank and using process-of-elimination. Found a valve tucked in a corner on a line coming out of the bottom of the tank. It didn't go to thte pump, so I figured this had to be the drain line. Opened it, and water started spilling out on the driveway.

My manual also had no relevant information.