Tool securing unloaded device behind washer (5)
I believe the answer is:
bidet
'washer' is the definition.
(thesaurus)
'tool securing unloaded device behind' is the wordplay.
'tool' becomes 'bit' (bit is a kind of tool).
'securing' indicates putting letters inside.
'behind' says to take the final letters.
The final letters of 'unloaded device' are 'de'.
'bit' going around 'de' is 'BIDET'.
(Other definitions for bidet that I've seen before include "Bathroom facility" , "Washing facility" , "Bathroom fixture" , "Low basin for washing private parts" , "Where to wash" .)