I recently installed a water pump for my uncle's refrigerator that uses 5-gallon water jugs as its source of water. The specific model is this: Flojet BW5000-000A Bottled Water System.

before installing my uncle had bought 5-gallon water jugs that rate threaded but we came to find out that the thought attached to the water jug didn't make a snug fit. So, I went ahead and designed an attachment that would make a tight seal around the threads.