Advice of mine sent back (3)
I believe the answer is:
tip
'advice' is the definition.
(thesaurus)
'mine sent back' is the wordplay.
'mine' becomes 'pit' (down the pit).
'sent back' shows that the letters should be reversed in order.
'pit' reversed gives 'TIP'.
'of' acts as a link.
(Other definitions for tip that I've seen before include "The rubbish dump" , "End - pourboire" , "for writers, it may be felt" , "Helpful suggestion" , "Extremity; gratuity" .)