Very good container, edge swapped around (6)
I believe the answer is:
tiptop
'very good' is the definition.
(tiptop can mean excellent)
'container edge swapped around' is the wordplay.
'container' becomes 'pot' (pot is a kind of container).
'edge' becomes 'pit'.
'swapped around' shows that the letters should be reversed in order.
'pot'+'pit'='potpit'
'potpit' back-to-front is 'TIPTOP'.
(Other definitions for tiptop that I've seen before include "cracking" , "Very fine" , "Best of its kind" , "The pinnacle of perfection" , "Excellent, super" .)