Drain soup for old poet (6)
I believe the answer is:
sappho
'old poet' is the definition.
(ancient Greek poet)
'drain soup' is the wordplay.
'drain' becomes 'sap' (synonyms).
'soup' becomes 'pho' (type of Vietnamese soup).
'sap'+'pho'='SAPPHO'
'for' is the link.
(Other definitions for sappho that I've seen before include "Sixth century BC Greek poetess" , "Greek female poet" , "Greek poetess; has pop (anag.)" , "Pa hops about Greek poet from Lesbos" , "Greek lyric poetess" .)