Inspire soldiers to wash outside (7)
I believe the answer is:
breathe
'inspire' is the definition.
(I know that inspire is a more specific form of breathe)
'soldiers to wash outside' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'to wash' becomes 'bathe' (I've seen this in another clue).
'outside' means one lot of letters goes inside another (some letters go outside others).
're' going within 'bathe' is 'BREATHE'.
(Other definitions for breathe that I've seen before include "Take into mouth" , "Whisper" , "Tell" , "Take inspiration" , "Express" .)