Talk of leak being suppressed by school (6)
I believe the answer is:
speech
'talk' is the definition.
(I've seen this before)
'leak being suppressed by school' is the wordplay.
'leak' becomes 'pee' (I've seen this in another clue).
'being suppressed by' indicates putting letters inside (I've seen this in other clues).
'school' becomes 'sch' (abbreviation).
'pee' inserted into 'sch' is 'SPEECH'.
'of' is the link.
(Other definitions for speech that I've seen before include "Formal address or discourse" , "Giving address" , "Verbal communication" , "Oration or talk" , "'Utterance, talk (6)'" .)