Posted under Tags
"Milk churn" is more specific and evokes the correct imagery for what the tags are used for. Just "milk can" could be confused with a normal type of can filled with milk or something. And I believe "milk churn" is more often used to refer to this that "milk can" is. +1 for milk_churn.
Updated
As a non-native speaker, I had to look up milk churn to see they really are the same. Then again, silly etymology doesn't really matter in what is more recognizable.
I'd go with churn. Milk can makes me think of an aluminium soda can with milk in it. A new tag can be created for butter churn if needed.