Large leaks from tanks affected people (4)
I believe the answer is:
fops
'affected people' is the definition.
(affected or pretentious people)
'large leaks from tanks' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'leaks from' is a deletion indicator (some letters leak out).
'tanks' becomes 'flops' (both can mean to fail).
'flops' with 'l' taken away is 'FOPS'.
(Other definitions for fops that I've seen before include "People affected" , "People concerned with appearance" , "Dandies, overdressed men" .)