Green’s Dictionary of Slang

(US) cheap, inferior whisky.

1945		R.L. Bellem ‘Coffin for a Coward’ in Hollywood Detective Dec. 🌐 I prowled the premises in search of [...] a snifter of varnish remover; there’s nothing like irrigating your tonsils to pass the time away.
c.2003		Foodbar.co.kr 🌐 ‘Favorite Egg Nog’ [...] As for the brandy, don’t waste the VSOP, but don’t use that buck-fifty-a-liter varnish remover that you picked up on that last trip to Tijuana, either.