Wash tin including large base (5)
I believe the answer is:
clean
'wash' is the definition.
(I know that wash is a more specific form of the action clean)
'tin including large base' is the wordplay.
'tin' becomes 'can' (synonyms).
'including' is an insertion indicator.
'large' becomes 'L' (eg in clothes sizes).
'base' becomes 'e' (Euler's number - base of natural logarithms).
'l'+'e'='le'
'can' placed around 'le' is 'CLEAN'.
(Other definitions for clean that I've seen before include "Clear (of drugs)" , "Not soiled, free from dirt" , "Honest" , "Non-polluting" , "Unsoiled" .)