It seems so obvious, right?, the connection between liquid dispensers. (And then just to make it all the more obvious, those awful comedies will have some poor actress holding two flagons of beer against her chest when someone says it). Well, apparently, the connection is so obvious that it's been made more than once in history.
According to this book, 'jugs' meant 'liquid holder/dispenser' (the type we all know), or 'tits' because of obvious linking connotations. The time Peter Silverton is talking about is the 17th Century.
More interesting, is he suggests that the original connection was made via an all-name for girls 'Jug', like Tom, Dick and Harry for boys.
Here's the quote:
"...Originally, the word 'jug' was short for Joan, derived the same way Sukie was from Susan and Jack from John... [later becoming a derogatory word for women]... An OED citation from 1569: 'dost though think I am a sixpenny jug?'
At some point, jug also came to mean a receptacle from which you can pour liquids. As these developments in meaning took place in a time when the written record is scanty, however, it's not clear how a word for women also became a word for a beaker with a spout and a handle. This is where OED makes the breast link, suggesting it's possible that it's an anatomical reference - that the jug we pour from is a word derived from a metonymical use of the jug that is everywoman.
...Then came the next lexical step, in more modern times. The word for the kitchen receptacle was metonymically linked back to the object (the breast) from which is originally derived its meaning. So Joan begat jug (nickname, via contraction) begat jug (everywoman, via generalisation) begat jug (kitchen receptacle, via metonymy) begat jug (breasts, again via metonymy). (Dick is similar. Dick, like Jug, first became a word for everyman, only then becoming a word for something every man has.)"
|From 'Five Anonymous Plays'|