Some discovered duck picked up milk container (5)
I believe the answer is:
udder
'milk container' is the definition.
(I've seen this in another clue)
'some discovered duck picked up' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'picked up' is a reversal indicator.
'reddu' can be found hidden inside 'discovered duck'.
'reddu' back-to-front is 'UDDER'.
(Other definitions for udder that I've seen before include "Steer with this" , "Animal mammary gland" , "Cow's milk source" , "Part of a cow" , "Milk supply" .)