The drain attaches to a "drain port" on the drip pan that's located in the top of the refrigerator section, directly under the fins. If you look to the left side of the drip pan you'll see the opening where the molded drain exits the interior of the refrigerator. On the outside, "tucked way up under the radiator fins" you'll find that drain port. There's a ribbed projection that the drain hose slips onto. It's routed down through the absorption tubing and then is routed out through one of the vent openings on the lower vent door.
In the end of the tube is a plug with several small holes in it. Without the plug in place, heat and bugs can crawl up the inside of the hose and enter your refrigerator. So, any hose will do, but remember to route it out of the trailer and use the plug in the end of the hose.
Here is one link to the drain hose plugs:
https://www.amazon.com/RV-Designer-E...2K0BWWE01RF9CQ