Green’s Dictionary of Slang

1. (N.Z. prison) liar [‘like a septic tank, a liar is ‘full of shit’’ Loooser (2001)].

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 162/1: septic tank n. 2 a liar .

2. (N.Z. prison) the solitary confinement cells.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 162/1: septic tank n. 3 = pound, the sense 1.