Green’s Dictionary of Slang

1. to drink.

[1708		J. Philips Cyder ii: Their frying blood compels to irrigate their dry-furred tongues].
1856		G.H. Derby Phoenixiana 104: He was invited by the urbane proprietor to irrigate.
1881		Greenock Advertiser 1 Oct. 4/1: The rancher slapped him on the shoulder and asked him if he would ‘irrigate,’ [...] ‘moisten your larynx,’ [...] ‘nominate your posion’.
1885		Bulletin (Sydney) 22 Aug. 14/3: ‘D’ye wait till ye’re thirsty before you drink?’ This idea seemed so amazingly ridiculous that the man thought it could have emanated from none but a new-chum, and he advised the Archdeacon to get back home again as he wouldn’t be a success out here if he didn’t irrigate.
1889		Music Hall & Theatre Rev. 16 Feb. 4/1: ‘shifter’ [writes] to the great and only Ally Sloper, concluding with an invitation to A.S. to come out and irrigate his larynx.
1893		W.K. Post Harvard Stories 246: The first rule was to assist each other in obtaining nourishment and irrigation at the crowded ‘spreads’.
1901		Bulletin (Sydney) 7 Dec. 19/4: The others proceeded to irrigate. The Soak’s thirst fought and conquered his bashfulness.
1907		C.E. Mulford Bar-20 iv: Come up an irrigate, old tank!
1916		Broadford Courier (Brisbane) 14 Apr. 1/4: There are many ways you can ask a friend to have a drink [...] ‘Will you irrigate’.
1925		Variety 26 Aug. n.p.: You come to drink. You recline pacifically and irrigate the tonsils.
1945		R.L. Bellem ‘Coffin for a Coward’ in Hollywood Detective Dec. 🌐 There’s nothing like irrigating your tonsils to pass the time away.
1951		Western Folklore X 81: [Barroom slang] The Act of Drinking . . . to irrigate the ulcers [DARE].

2. to give a drink to someone else.

1906		Sun. Times (Perth) 24 June 4/7: ‘I’m in favour of a Goddam drink before we start.’ (Car steward still further irrigates the already shickered company).
1907		C.E. Mulford Bar-20 vi: After he had irrigated several square feet of parched throats belonging to the audience he again took up his journey.