I just took the back freezer panel off exposing the coil and cleared the ice with hot water and a hair dryer. There is no chance for ice to be present at this point. I have gotten this far before but days later the ice block returns. I am unable to verify that the drain is actually clear. It doesn't appear that I have any access to a drain tube from the back as you suggested.

It seems this is the limit to my understanding of the system. When the water drains down to the pan, is there a way to further empty the evaporator pan? For all I know at this point the pan is full. I looked underneath as best I could to find some way to check for water. I am stuck.

(added) okay just found a vertical rubber hose approx 10" long near the fan in the back. I pulled it off the connector at the bottom and a couple drops of dirty brown water came out. It was clogged. I cleaned the tube and water flows freely from inside freezer through tube. Thanks for the help.