Green’s Dictionary of Slang

(Aus.) a light-fingered person, who’ll ‘lift anything that isn’t nailed down’.

1960		Bulletin 13 Apr. 10: His first name being Jack, he was called by his mates ‘Hydraulic Jack’ – because, it was explained to me, he’d lift anything.
1977		Sunday Tel. (Sydney) 24 Apr. 136: They call him Hydraulic – he’ll lift anything that isn’t nailed down [GAW4].
2021		Betoota-isms 67: Hydraulic [...] 1. Someone who will steal (lift) anything.