As others have said it is a drain. Make sure the tube stays in place. Factory left mine loose and I had water problems before I figured out where the water was coming from. Factory fixed the damage along with the lack of support for the slide.
'01 Dodge 3500 CTD, Lance 1121, Air Bags, Rancho 9000, All Wheels Under Power When Needed, A Few Engine Mods For Increased HP
Burning Grease, 800 ft/lbs. of torque from something you throw away.