Following down to a trickle (4)
I believe the answer is:
flow
'to a trickle' is the definition.
(I've seen this before)
'following down' is the wordplay.
'following' becomes 'f.' (used when citing page numbers etc).
'down' becomes 'low' (associated in meaning).
'f'+'low'='FLOW'
(Other definitions for flow that I've seen before include "Run or move like a liquid" , "Scapa - , Orkney anchorage" , "Run smoothly" , "Trickle" , "Uninterrupted stream" .)