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The water from the outside should be able to build up toward the inside of the unit. Make sure the unit is sloped toward the outside. In other words, the outside portion of the unit should be lower than the inside. This will cause the water to drain to the outside, and out the drain hole as it should. If the unit is dirty, with leaves, and other debree, then you may need to take the unit out side, and spray it down with the garden hose and clean it up. Allow a couple hours for it to dry before plugging the unit back up, try to avoid spraying the controls, that will help. If this information has assisted you, please give me a god to great rating.....Thank you