Is to run outside for a metal container (8)
I believe the answer is:
canister
'a metal container' is the definition.
(I've seen this before)
'is to run outside' is the wordplay.
'to run' becomes 'canter' (I've seen this before).
'outside' indicates putting letters inside.
'is' inserted inside 'canter' is 'CANISTER'.
'for' is the link.
(Other definitions for canister that I've seen before include "Metal food container" , "Metal box" , "Vessel" , "Container for storing dry food" , "Container for e.g. tea" .)