Tip about mine (3)
I believe the answer is:
pit
'mine' is the definition.
(down the pit)
'tip about' is the wordplay.
'about' says the letters should be written in reverse.
'tip' back-to-front is 'PIT'.
(Other definitions for pit that I've seen before include "A hole as for coal" , "Tip into hole" , "Tip into crater" , "Cherry stone" , "Where the orchestra sits at an opera" .)