Maximum taken in drink, spit it out! (5,2)
I believe the answer is:
speak up
'spit it out' is the definition.
'maximum taken in drink' is the wordplay.
'maximum' becomes 'peak' ('peak' can be similar in meaning to 'maximum').
'taken in' means one lot of letters goes inside another.
'drink' becomes 'sup' (I've seen this before).
'peak' put into 'sup' is 'SPEAK UP'.
(Other definitions for speak up that I've seen before include "Raise one's voice" , "Raise your voice - can't hear you" , "Make oneself heard" , "give opinions boldly" , "augment volume" .)