Originally Posted by summer home
My 375FL has the same drain... it is for the icemaker supply line
I think this is your answer. I have the 3731FL also. Manual says to turn off ice maker in freezing weather as the water line has exposed section to the slide. There should be a water shutoff under the sink that you close and then open that drain to remove any water that's In the line. Mine was in the center of the underbelly so I added an elbow and section of pex clamped to the drivers side near the convenience center. I didn't want to have to crawl under to drain that in freezing and maybe snowy weather.
2017 Lariat F-350 FX4, CC, SB, 6.7 PSD 4WD
2018 MONTY 3731FL, Residential Refer