Swill (4)
I believe the answer is:
slop
'swill' is the definition.
(I know that swill can be written as slop)
This is all the clue.
(Other definitions for slop that I've seen before include "(Of liquid) spill over" , "Cause to spill over" , "Liquid refuse, swill" , "Household liquid refuse" , "discarded > loose garment" .)