Small storage facility in Slough (4)
I believe the answer is:
shed
I believe this clue is a double definition.
'small storage facility' is the first definition.
(storage facility in a garden)
'slough' is the second definition.
(both can mean to discard something)
'in' is the link.
(Other definitions for shed that I've seen before include "One-storeyed outbuilding" , "storage facility" , "dropped" , "place for bikes" , "Discarded" .)