Lightly wash back of cooker in quarters (5)
I believe the answer is:
rinse
'lightly wash' is the definition.
'back of cooker in quarters' is the wordplay.
'back of' says to take the final letters.
'quarters' becomes 'se' (**).
The final letter of 'cooker' is 'r'.
'r'+'in'+'se'='RINSE'
(Other definitions for rinse that I've seen before include "blue one on top?" , "Sluice" , "Wash without using soap" , "Wash - siren (anag)" , "Colour" .)