Discharge gas put through drink (5)
I believe the answer is:
rheum
'discharge' is the definition.
(I know that rheum is a type of discharge)
'gas put through drink' is the wordplay.
'gas' becomes 'He' (chemical symbol for helium).
'put through' means one lot of letters goes inside another.
'drink' becomes 'rum' (rum is a kind of drink).
'he' inserted within 'rum' is 'RHEUM'.
(Other definitions for rheum that I've seen before include "nasal drops" , "sign of illness" , "drips from the nose" , "Flowing water" , "Watery discharge; sounds like space" .)