Green’s Dictionary of Slang

to tape the penis to the groin (usu. in the context of transvestism).

1985		T.R. Houser Central Sl. 53: tuck [...] ‘Before I come out on the streets, I tuck, and the men love it.’.
1993–2003		D. Gulliver on Urban Dict. 🌐 tuck when a male does a tuck, he ‘tucks’ his penis and testes back through his legs which encompasses the look of a females genitals. does it look better tucked or untucked?