Water backing up into Refrigerator Freezer
I have had this issue myself. I had a good service tech who explained the issue and said if he fixed it the cost would be $300. Or he could explain how to fix for it $75. You have already figured out how to take the freezer apart. I used a turkey baster with a small hose attached to force warm water down the drain. After the water cools suck it out with the baster and replace it with more warm water. When the drain is completely free the water should flow through and collect in the drain pan under the fridge.