What Eric F said.
That line drains the condensate from the little drip tray under your refrigerator's aluminum fins inside the fridge to outside the trailer. Make sure it does not get pushed back behind the refrigerator access door, that it stays "outside". That way the water does not eventually cause mold and rot problems.
Enjoy the new rig and have fun.
Chris from Virginia
2006 Sunseeker 3100SS/LTD
2008 Smart Passion Cabriolet TOAD
1986 Honda Helix (Original owner)