Crazy procedure to seal ends of cask (5)
I believe the answer is:
wacky
'crazy' is the definition.
(I've seen this before)
'procedure to seal ends of cask' is the wordplay.
'procedure' becomes 'way' (I've seen this in another clue).
'to seal' indicates putting letters inside.
'ends of' says to hollow out the word (remove centre letters).
'cask' with its middle removed is 'ck'.
'way' enclosing 'ck' is 'WACKY'.
(Other definitions for wacky that I've seen before include "Oddly amusing (colloq.)" , "Eccentric - erratic" , "Weirdly funny" , "Oddly crazy" , "Funny in a peculiar way" .)