Medic on the brink with last bit of paper - it's used to clean bottoms (7)
I believe the answer is:
dredger
'it's used to clean bottoms' is the definition.
(a dredger cleans the bottom of a harbour)
'medic on the brink with last bit of paper' is the wordplay.
'medic' becomes 'dr' (doctor).
'on' is a charade indicator (letters next to each other).
'the brink' becomes 'edge' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'last bit of' suggests the final letters.
The last letter of 'paper' is 'r'.
'dr'+'edge'+'r'='DREDGER'
(Other definitions for dredger that I've seen before include "Vessel for dragging the bottom" , "one scooping out unwanted material" , "Waterway excavator" , "Sugar container" , "Boat for deepening waterways" .)