[Closed] Fridge Experts...

Our kitchen has an inbuilt fridge (which was there when we bought the house), however the little drain out the back keeps freezing over (the fridge is not very cold)and the bottom fills with water. All my other fridges had a little bit of plastic in the hole that I assume was there to stop this freezing happening. Did this bit of plastic stop the frost build up? If so can you get them separately and retrofit? What are they called? Can I make one out of anything else? It seems to be clogging up every couple of weeks and I don't really want to turn the fridge temperature down any more.