Green’s Dictionary of Slang

squat n.1

1. [late 19C–1910s] a seat, a chair.

2. [1950s] (US teen) the vagina [? deliberate euph. for twat n. (1)].

3. [1970s] (US) an act of defecation; also, of women, an act of urination.

4. [1970s+] (US) excrement.

5. [1990s+] (US prison) the electric chair; electrocution.

In phrases

take a squat (v.)

[1970s+] to defecate.