Suckers (4)
'suckers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for saps that I've seen before include "mugs" , "Weakens, deprives of energy" , "Pass around foolish people" , "trenches" , "Vital juices" .)
(Another definition for vacs that I've seen is " Holidays (abbreviation); rhymes with 9ac".)