Green’s Dictionary of Slang

tin tank n.

a bank.

1932		‘P.P.’ Rhy. Sl. 5: I’m going to the ‘tin tank’ to draw some ‘Oscar Ashe.’.
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 11: Tin tank: Bank.
1953		T.A.G. Hungerford Riverslake 143: Hide it well until you can get it into the tin-tank.
1960		J. Franklyn Dict. of Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 49: Tin Tank Bank.