Spill valve discovered in this place (5)
I believe the answer is:
taper
'spill' is the definition.
(I've seen this before)
'valve discovered in this place' is the wordplay.
'valve' becomes 'tap'.
'discovered' says to take the centre.
'in this place' becomes 'here' (synonyms).
The central letters of 'here' are 'er'.
'tap'+'er'='TAPER'
(Other definitions for taper that I've seen before include "Become thinner towards one end" , "Thin wick" , "Get thinner - lighter" , "Gradually reduce - spill" , "On VHS he recorded" .)