Green’s Dictionary of Slang

1. dismissal from a job [sack n. (2a)].

1932		‘P.P.’ Rhy. Sl. 15: When pore old Jim got the ‘Tin tack’ ’E went aht and got ‘Elephant’s trunk.’.
1960		J. Franklyn Dict. of Rhy. Sl.

2. a bed [sack n. (4)].

2002

D. Shaw ‘Dead Beard’ at www.asstr.org 🌐 She fits against me in all the right places and it would be great to be in the tin tack with her but I’ll deal with her in the bushes, even if it is a bit brian clough.