Green’s Dictionary of Slang

(US) sticky, viscous; messed up with or looking like gunk.

1971		Current Sl. VI 6: Gunky, adj. undesirable.
1999		Indep. Mag. 12 June 24: He wants to see just how gunky your ketchup bottle gets before you chuck it away.
2001		J. Stahl Plainclothes Naked (2002) 241: Tony sucked in a lung-numbing hit — there was some gunky resin lodged in the bottom [of the crack pipe].
2009		L. McIlvanney All the Colours 20: For me, in any case, the gunky bottles said it all.