Dept. of ad nauseum
Origins and meanings were discussed in great detail (excessive) in thread 3116, as noted in a previous post:
Origins Whiskey

The phrase was not in the original songs
The phrase appears in 19th c. music hall versions, recorded in broadsides, in several forms.
As Malcolm Douglas remarked (thread 3116): "Although it's possible that the chorus may have some meaning on the lines of some of the ingenious suggestions made ..., it's probably just as likely that it's meaningless 'cod Irish' of the music-hall variety."