Clown and I make a mistake filling container (7)
I believe the answer is:
pierrot
'clown' is the definition.
(I've seen this before)
'i make a mistake filling container' is the wordplay.
'make a mistake' becomes 'err' ('err' can be a synonym of 'make a mistake').
'filling' is an insertion indicator.
'container' becomes 'pot' (pot is a kind of container**).
'i'+'err'='ierr'
'ierr' inserted into 'pot' is 'PIERROT'.
'and' acts as a link.
(Other definitions for pierrot that I've seen before include "French panto clown with whitened face" , "In French panto, clown with white face and baggy costume" , "Seaside clown" , "French stage character with white face and costume" , "Male clown from French pantomime" .)