A taste from the siphon (3)

I believe the answer is:

sip

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'a taste' is the definition.
(I've seen this in another clue)

I don't understand the remainder of the clue.

(Other definitions for sip that I've seen before include "Drink, small mouthful" , "Small mouthful of fluid" , "Thimbleful" , "Take small mouthfuls of (drink)" , "Small mouthful of liquid" .)

I've seen this clue in the Evening Standard.

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