Glad you figured this out. So it is the low point drain for your fresh or potable water tank. Is it a threaded cap type or quarter turn valve? If it is a threaded cap type fitting you might want to keep a spare or 2 on hand. The fresh tank on our 2012 36RL is pretty far up front and we broke the water drain line off of the tank when hitting something while on the road. Had to remove the coraplast underbelly and plumb in a new drain line and fitting. Easy.
Chris & Maria
2012 36RL, Full Body Paint, Dual Awning, Dual a/c, Splendide Combo, Fisher Paykel dishwasher, 6.5kW Onan, Goodyear G614's. 2015 F550 6.7l, 4X4, Lariat, CC, 176" WB, Long Box, B&W Companion