Green’s Dictionary of Slang

a heavy drinker.

1912		Bulletin (Sydney) 1 Aug. 15: Go and Gone. / Hebe: ‘But you always said you liked a woman with a certain amount of go about her.’ / Tanker: ‘Yes, but it’s different. You see, my wife has gone with another man.’.
1936		W.W. Williams Quiet Lodger of Irving Place 69: The Club regulars were not café loafers, ‘bar-flies’ and ‘tankers’; all of them were young men, with few exceptions, holding good positions.