Suggestion: mine is taken up (3)
I believe the answer is:
tip
'suggestion' is the definition.
(tip is a kind of suggestion)
'mine is taken up' is the wordplay.
'mine' becomes 'pit' (down the pit).
'is taken up' is a reversal indicator.
'pit' reversed gives 'TIP'.
(Other definitions for tip that I've seen before include "offered at end of repast" , "Piece of useful advice" , "single piece of asparagus, perhaps" , "present!" , "Point; sweetener" .)