More than likely it's going to take some heat before you can drain it out.

It MAY only require the use of a small propane torch. BUT if there are any plastic parts on the drain, I would definitely avoid doing it that way.

You could possibly use an electric space heater aimed toward the valve.

Any way you thaw this out remember that as the air/fluid starts coming out the rush of air may freeze it back closed. It may take a few rounds of heat and drain to get it all out.

Hope this helps.