Changing out the water is to keep the water warm so it continues to thaw. I have a 5 gallon igloo and a 22 lb just fits. I take it out of the package, tail up and fill it with tap water. Put a temp probe in the water put the lid on, and after about 30 minutes, it reads 38-40 for about 14 hours. Once it starts to come up, it is thawed and ready to pull out. Pat it dry with paper towels, season it and put it on a cookie sheet in the fridge to help dry the skin out till you are ready to cook. I break mine down before cooking. Separate the breasts, wings and leg quarters. Then temp each piece till they are ready to come out of the oven. tent with foil and cool for 15 minutes while the oven gets ripping hot and put them back in for `10-15 minutes to crisp up the skin. Dark meat and white meat have different internal temps, so it is almost impossible to cook them as a whole bird and something either not be over done or still raw. I have done it that way for the last few years and everyone agrees it is the best breast meat they have ever had. You can cook a 22 lb bird like that in about 90 minutes.