I don't remember ever seeing a drain on them.
What I have done is disconnect the hot and cold water lines so they can drain. Disconnect the drain/discharge hose and then pour some non toxic anti freeze directly into the washer. You will have to run a wash cycle through when you want to bring it back into service.
2008 Cruiser CF26RK
2013 Ford Eco-Boost
Heavy duty payload - Max tow