Green’s Dictionary of Slang

peep v.4

SE in slang uses

In phrases

peep in the heater (v.)

(US) to perform cunnilingus.

[US]‘Mae West in “The Hip Flipper”’ [comic strip] in B. Adelman Tijuana Bibles (1997) 95: He had commenced to enjoy peeping in the heater.
peep through one’s liquor (v.)

(US black) to pose as sober when one is in fact drunk.

[US]Z.N. Hurston ‘Story in Harlem Sl.’ in Novels and Stories (1995) 1009/2: Peeping through my likkers — carrying on even though drunk.