|Kolton Olson added|
Update: a video of a dairy back when milk was delivered with cans rather than bulk milk trucks. First they unload them. Do they weigh and sample each can or a batch of all the cans that came from one farm? The later would require some sort of marking and more careful placement in the box car of the "milk run" trains. Then you can see them putting the cans in and out of the washer. I wish someone would narrate it. I can guess what some of the equipment is. For example, I think the big round tank with a lid is a pasteurizer. I was surprised to see that a dairy would have a lathe.
|Screenshot at -1.22|
This shows that they do keep track of which cans came from which farm.
At 1:03 in this video, you can see someone pulling a cart with at leasat three milk cans getting ready to put them on the arriving train.