Get rid of drainage facility (5)
I believe the answer is:
ditch
I believe this clue is a double definition.
'get rid' is the first definition.
(I've seen this before)
'drainage facility' is the second definition.
(a ditch may be part of a drainage system)
'of' is the link.
(Other definitions for ditch that I've seen before include "Scrap" , "Drainage channel" , "Drop" , "side of field?" , "Abandon; one dug" .)