When I get a good deal on milk, or for some reason don’t want to have to make a trip to the store for a few days, I freeze my milk. The containers that they come in from the store have the indentations on the sides that will expand when the milk freezes. I don’t normally pour any out when I freeze it.
To unthaw, I just put mine in the fridge or in a warm sink of water for an hour or so.
When the milk is unthawed you will want to shake it really well as it usually separates a bit when frozen. My kids don’t mind it at all having been frozen. Every now and then it will get a little “grainy” and since we usually use it for cereal no one notices.
If your milk looks like it is too close to the top, you should pour a little out. The recommended amount is about 1/2 cup per 1 gallon.