Green’s Dictionary of Slang

(Aus.) poor quality tea, with particles of stalk and other impurities floating on its surface; such impurities may have been deliberately added to bulk out a grocer’s measure.

1851		Australasian 298: Hyson-skin and post-and-rail tea have been superseded by Mocha, claret, and cognac.
1858		‘A. Pendragon’ Queen of the South 19: There’s other post and rails than them made of stringy bark; there’s a sorter tea, coarse as chips and bitter as hops.
1870		T.H. Braim New Homes 28: The shepherd’s wife kindly gave us the invariable mutton-chop and damper, and some post-and-rail tea.
1883		J. Keighley Who are You? 36: Then took a drink of tea ... Such as the swagmen in our goodly land Have with some humour named the post-and-rail.
1887		‘Aus. Colloquialisms’ in All Year Round 30 July 66/2: The tea [...] is naturally of rather a rough-and-ready description, and when the stalks and coarse particles of the fragrant leaf float thickly thereon, it is sometimes graphically styled ‘post-and-rails’ tea .
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.].
1908		G. Seagram Bushman All 262: The jackshays were boiled and under the soothing influence of ‘post and rail’ [...] their ordinary natures resumed control.
1910		Bulletin (Sydney) 21 July 30/2: When Bill toils hard on the dear old farm for a quid per week, and found, / Free pumpkins, sinkers and post-and-rail on the groaning board abound; / Aye, the groaning board of the farmer’s stocked with a mountain of good plain fare, / To go with the fine large wage he pays – if the toiler will do his share.
1936		A. Russell Gone Nomad 24: Flour, ‘post and rail’ tea [...] salt and meat, were the only rations provided.
1945		Baker Aus. Lang. 83: Post-and-rails (also called post-and-rail tea) [...] derived from the pieces of stalk and leaf floating on top.