Let go of container on the way up — about right (4)
I believe the answer is:
drop
'let go of' is the definition.
'container on the way up about right' is the wordplay.
'container' becomes 'pod' (pod is a kind of container).
'on the way up' shows that the letters should be reversed in order.
'about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'pod' backwards is 'dop'.
'dop' enclosing 'r' is 'DROP'.
(Other definitions for drop that I've seen before include "Tiny bit of liquid" , "sack" , "Fall down with liquid globule" , "Plunge" , "Decline - fall" .)