Very little pressure creates leak (4)
I believe the answer is:
weep
'leak' is the definition.
(I've seen this before)
'very little pressure' is the wordplay.
'very little' becomes 'wee' (I've seen this in another clue).
'pressure' becomes 'p' (abbreviation).
'wee'+'p'='WEEP'
'creates' acts as a link.
(Other definitions for weep that I've seen before include "Display sorrow" , "Express grief or sorrow" , "leak" , "lament" , "Seep slowly out" .)