The drain comes out the side of the fresh water tank. It's just a small plastic/pex tube, and should be extending down thru the black membrane covering the bottom of the trailer. It will only be sticking thru a small amount. Look a little closer. Don't be looking for a big ol plug, just a small tube.
One other thing.
If you don't list the make and model of your camper in your sig. you should state what it is when asking for assistance. It might help us figure out what is wrong.
2008 Cruiser CF26RK
2013 Ford Eco-Boost
Heavy duty payload - Max tow