Bolt low within water-filled vessel (7)
I believe the answer is:
vamoose
'bolt' is the definition.
(both can mean to run away or leave)
'low within water-filled vessel' is the wordplay.
'low' becomes 'moo' (both can mean to make the noise of a cow).
'within' means one lot of letters goes inside another.
'water-filled vessel' becomes 'vase'.
'moo' put within 'vase' is 'VAMOOSE'.
(Other definitions for vamoose that I've seen before include "Beat it" , "Scram!" , "scarper" , "vanish" , "Shoo!" .)