Actually, there are two of them mid passenger side. The one between the peg board bay and the bay just in front of it is the water tank drain. A little further forward of that is another drain. On mine, it's along the latch side of the door frame on the pass thru bay. I believe that is for the A/C, but have never seen it drain any water.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor