Rinse out warning device (5)
I believe the answer is:
Here is my best explanation:
'warning device' is the definition.
(I've seen this before)
'rinse out' is the subsidiary indication.
'out' is an anagram indicator.
'rinse' with letters rearranged gives 'siren'.
(Other definitions for siren that I've seen before include "Bewitching singer,part- woman, part-bird", "Loud whistle for sea temptress", "Seductive woman", "Loud warning signal", "Rinse (anag) - sea nymph", "Alluring female", "Vamp; alarm", "Seductress", "Loud whistle or sea witch" and "Risen like Lorelei".)