Loss of liquid from evaporation or leakage (6)

I believe the answer is:

ullage

(Other definitions for ullage that I've seen before include "Loss by evaporation or leakage" , "Amount by which a liquid container falls short of being full" , "The amount by which a bottle falls short of being full" , "shortfall" , "dregs" .)

I've seen this clue in The Guardian.

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