Without pressure, clears out drives (5)
I believe the answer is:
urges
'drives' is the definition.
(I've seen this before)
'without pressure clears out' is the wordplay.
'without' is a deletion indicator.
'pressure' becomes 'p' (abbreviation).
'clears out' becomes 'purges' (I've seen this before).
'purges' with 'p' removed is 'URGES'.
(Other definitions for urges that I've seen before include "Drives" , "Inner promptings" , "Exhorts or prods" , "Encourages" , "Compulsions" .)