I was called out to this after a friend was out clearing the fresh food section drain. I found exactly what he reported: The drain was frozen but the clog was about a foot down the drain, about at the line between freezer and fridge. I got it clear and then found these duckbills on both drains. The duckbill with the chunk out of it is the FF one. I just pinched it with my fingers and it ended up like that. This looks like the fix for the Whirlpools before we heard of the p-trap. I made sure the drain was rooted out and with the notch out of the duckbill, I'm thinking it will be okay.
Is there something else I need to do to make sure the drain stays open? There's already a strip of aluminum around the heater, at the opening of the drain.