Swabs in thermos indicate presence of wormwood in drink (8)

I believe the answer is:

absinthe

I'm a little stuck... Click here to teach me more about this clue!

'drink' is the definition.
(absinthe is a kind of drink)

'swabs in thermos indicate presence of wormwood' is the wordplay.
'ABSINTHE' is hidden within the letters.
However, I am unsure how the hidden word is indicated.

'in' is the link.

Can you help me to learn more?

(Other definitions for absinthe that I've seen before include "Strong green liqueur, lethal when made with wormwood" , "Green aniseed liqueur" , "Aniseed-flavoured liqueur" , "Liqueur - the basin (anag)" , "Liqueur originally containing wormwood" .)

I've seen this clue in The Irish Times.

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