Stand up to grab bottom of chain for flush (5)
I believe the answer is:
rinse
'for flush' is the definition.
(I've seen this before)
'stand up to grab bottom of chain' is the wordplay.
'stand up' becomes 'rise' (synonyms).
'to grab' means one lot of letters goes inside another.
'bottom of' indicates one should take the final letters.
The final letter of 'chain' is 'n'.
'rise' enclosing 'n' is 'RINSE'.
(Other definitions for rinse that I've seen before include "Flush" , "Hair preparation" , "Remove soap with clean water" , "Cleanse in water" , "Wash - siren (anag)" .)