Sound of sucker in drain (5)
I believe the answer is:
leach
'drain' is the definition.
(I've seen this before)
'sound of sucker' is the wordplay.
'sound of' shows a homophone (sound like).
'sucker' becomes 'leech' (I've seen this in another clue).
'leech' sounds like 'LEACH'.
'in' is the link.
(Other definitions for leach that I've seen before include "Remove (soluble material) by percolation" , "Percolate - be removed by percolating liquid" , "Make liquid percolate through a solid" , "Make liquid percolate through soil" , "Drain away through percolating liquid" .)