Foe failed to finish with a washout? (5)
I believe the answer is:
enema
'washout?' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for enema that I've seen before include "treatment by rear entrance" , "Procedure for vacating the bowels" , "Suppository" , "medicine to get you going" , "Fluid injected rectally" .)