A long narrow trough is best for feeding to allow enough bunk space. All hogs in in group will all drink at once. Steel trough or plastic barrels split lengthwise with a Sawzall can be used. Some folks take old steel water pressure tanks and split them lengthwise with a torch.
15 gallon plastic barrels or 5 gallon pails with lids can work for transporting.
For hogs over 60 pounds on the hoof, a gallon/day/pig more or less seems to work out fine when coupled with grain feed.
In cooler months from now till spring milk can be stored for hog feed without refrigeration for up to 5-7 days. Some curdling may occur, with no ill effect on hogs. You do not state your geographic location. Freezing may require storage above 32F so you can dispense a liquid product.
When you say approaching a dairy, I am unclear if you mean a dairy manufacturing plant or a dairy farm?
We only use milk from our dairy herd, so I cannot advise as to value assigned to it.