All refrigeration units create condensation which has to drain off somewhere. A/C units have a little drain pan with drain tubes to the underside of the car. Ever notice the puddle of water under your parked car after you've used the A/C? I don't know what brand refrigerator you have in your house, but if you pull the little grill at the bottom, you'll find a tray you can pull out and there will be water in it. In a kitchen that doesn't move except sometimes out here in California the water evaporates faster than it fills the pan so no drain hoses required. Cars are moving and would slosh water. Hope that answers the question.
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