A drink that is diluted and cast out (6)
I believe the answer is:
shandy
'a drink that is diluted' is the definition.
'shandy' can be an answer for 'a drink' (shandy is a kind of drink). I'm unsure of the remainder of the definition.
'and cast out' is the wordplay.
'cast' becomes 'shy' (both can mean to throw or fling).
'out' is an insertion indicator.
'and' inserted into 'shy' is 'SHANDY'.
Can you help me to learn more?
(Other definitions for shandy that I've seen before include "A misture of ale and lemonade" , "mixed drink" , "Beer and lemonade mixture" , "Beer/lemonade drink" , "Beer-lemonade mix" .)