Mine’s an untidy place on reflection! (3)
I believe the answer is:
pit
'mine's' is the definition.
(down the pit)
'place on reflection' is the wordplay.
'place' becomes 'tip' (tip is a kind of place).
'on reflection' says the letters should be written backwards.
'tip' backwards is 'PIT'.
'an untidy' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for pit that I've seen before include "Tip into miners' shaft" , "Sizeable hole in the ground" , "Large hole; fruit stone" , "Cherry-stone" , "Large hole; mine" .)