Swallows singular fluids (5)
I believe the answer is:
sinks
'swallows' is the definition.
(sink can mean to swallow or drink)
'singular fluids' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'fluids' becomes 'inks' (ink is a kind of fluid).
's'+'inks'='SINKS'
(Other definitions for sinks that I've seen before include "Basins" , "Goes down" , "Dips" , "Scuttles" , "Declines markedly" .)