Depending on the area of the country you live in, you may be experiencing high humidity within your home. This will be drawn out of the air by the coils of the fridge, drain back into the pan causing it to overflow. For instance: I live in S. Georgia, high humidity here always. I run a de-humidifier at night and it is not unusual for it to fill the one-gallon container in less than 8 hrs.
A word of caution here to anyone who has a fridge in a garage, shop, where mosquito's can access the area. I have found that the evaporator pan is a wonderful breeding ground for mosquito's. The warm water in them is something they love, especially those pans that sit right on the compressors. Ask me how I learned this. David