De-iced freezer drain but repeatedly freezes over

Water leaking inside fridge from freezer. Lots of ice around drain. Have done the turkey baster with hot water 3x which lasts about 3 weeks before refreezing up again. Also tried a copper wire from heater inside drain line. Could it be a bad thermostat? or timer? There was a 6-8" dia puddle of water on my freezer the other day before it froze up.