Freezer Drain?

My freezer drain that drains defrosted water down to the evaporated pan in the bottom of my Model 78202891, frig. continues to freeze up. It then causes ice to form below the bottom slide out tray in the freezer. I have removed the ice twice from the drain tube and poured water down it to be sure it is clear, but it freezes up again. Once the drain tube is frozen water will run into the refrigerator area. What do I need to try next.