Device that prevents pouring out of claret (10)
I believe the answer is:
tourniquet
'device' is the definition.
(I have seen 'Medical device' mean 'tourniquet' so perhaps 'device' could also mean 'tourniquet')
'prevents pouring out of claret' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'out' is 'tou' which is within the answer.
This may be the basis of clue (or it may be nonsense).
'that' acts as a link.
Can you help me to learn more?
(Other definitions for tourniquet that I've seen before include "it'll stop bleeding" , "Device for stopping blood flow" , "medical treatment" , "Compression bandage" , "Appliance used to stop bleeding" .)