Our moderately old (5 years?) top-freezer Whirlpool regularly freezes its drain hose shut. In theory, the auto defrost goes on now and then, the built-up ice melts and runs down the drain hose to the drip pan underneath and the water evaporates. In practice, that works for a few days, then the drain hole in back of the freezer gets blocked with ice and eventually the melt water backs up, overflows the freezer and floods the bottom of the fridge until it runs out on the floor. Every few weeks I have to empty the freezer, pull off the plastic panels and flush the hose with hot water in a turkey baster. Once it's clear it works all right for a few days, then the process starts over. My general appliance repair manual explains what to do about the immediate problem but doesn't give a cause or permanent fix. Anybody have a clue?