The reason for associating the aphid with milk is, of course, because a variety of ant and a variety of aphid have a mutualistic relationship in which the ants protect the aphids from predators and the aphids respond to the ants by excreting a sugary substance, and this relationship has been compared to that of dairy farmers with the beasts from which they get milk.
The best thing that I've found for dealing with aphids are ladybugs. Placed on a plant, the ladybugs will make a systematic search for prey, and will thus clean it of aphids.