I use a food grade, 4 gallon (15 liter) plastic bucket. The milk is already chilled when I pick it up and I keep it cold, even in the hot DC summer, by putting it on ice in a cooler filled up with ice. I've put a thermometer in the milk after keeping it on ice on my patio (I don't have a large enough fridge for it) on a hot summer night and it was 38 degrees, a decent temperature to inhibit pathogen growth. I believe the state health rules and the cooperative's regs for my parents' cow dairy require the milk to be kept between 35-40 degrees prior to pick-up by the hauler, so this seems to work well, especially because I never use milk more than 48 hours old. In general, I'd say the closer to 33 degrees you can keep the milk the better (without freezing, of course, that's a rancid-causing disaster for cow and goat milk, but apparently not a big problem for sheep's milk).
Hope that's helpful.