Throw water on function twice (5)
I believe the answer is:
douse
'throw water on' is the definition.
(I've seen this in another clue)
'function twice' is the wordplay.
'function twice' can mean two replacements for 'function'.
'function' becomes 'do' (both can mean an event).
'function' becomes 'use' (something's use is its function).
'do'+'use'='DOUSE'
(Other definitions for douse that I've seen before include "heavy blow" , "Throw water over, extinguish" , "Smother with water" , "Soak" , "Plunge into water" .)