ullage, n. — Green’s Dictionary of Slang

ullage n.

[SE ullage, the amount of wine or other liquor by which a cask or bottle falls short of being quite full; note WWI RN ullage, an incompetent]

the dregs in the bottom of wine glasses or casks.

1873		Sl. Dict. 332: Ullages, the wine of all sorts left in the bottoms of glasses at a public dinner.
1890–1904		Farmer & Henley Sl. and Its Analogues.