Channel crossing finally complete (6)
I believe the answer is:
gutter
'channel' is the definition.
(I know that gutter is a type of channel)
'crossing finally complete' is the wordplay.
'finally' says to take the final letters.
'complete' becomes 'utter' (both can mean total).
The last letter of 'crossing' is 'g'.
'g'+'utter'='GUTTER'
(Other definitions for gutter that I've seen before include "Roadside channel" , "Threaten to go out" , "Street channel for carrying off rainwater" , "Someone removing contents" , "Person who empties" .)