Green’s Dictionary of Slang

(Aus.) (tomato) sauce.

1918		Alpine Obs. (Vic.) 26 Apr. 3/2: ‘I can't understand these men [...] They are all calling out, “We can't eat up the skies without some dead horse”.’ A veteran voluntary worker smiled. ‘You’ll have to learn the new Australian language my dear,’ she said. ‘The boys are only asking for tomato sauce for their pies’.
1940		Standard (Frankston, Vic.) 26 July 26/2: ‘The dead horse, you blank fool — in that bottle!’ I woke up at last — he was referring to the tomato sauce.
1941		Aus. Women’s Wkly 26 July 22/2: The rhyming slang of the Cockneys still has its adherents [...] ‘dead horse’ for tomato sauce.
1952		Border Watch Mt Gambier, SA) 29 Apr. 12/2: One of the lads asked for the sauce, and the word was passed down from one to the other. Eventually one of them called to a companion, ‘Pass up the dead horse.’.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxiv 4/3: dead horse: Sauce. Also rockin’ horse.
1975		Canberra TImes (ACT) 5 Feb. 13: [Sausages were] stabbed and dipped in a bowl of ‘dead horse’ Australian rhyming slang for tomato sauce.
1984		V. Darroch On Coast 75: Dead horse: Sauce.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 53/2: dead horse n. sauce.
2002		Pete’s Aussie Sl. Home Page 🌐 dead horse: sauce.
2016		N. Cummins Adventures of the Honey Badger [ebook] The orders [...] usually consisted of a rat coffin or a leper in a sleeping bag (sausage rolls), maggot bag, dog’s eye or mystery bag (pies), dead horse (tomato sauce) and battery acid (cola).