Arrive and wash and confess fully (4,5)
I believe the answer is:
come clean
'confess fully' is the definition.
(I've seen this before)
'arrive and wash' is the wordplay.
'arrive' becomes 'come' (synonyms).
'and' means one lot of letters go next to another.
'wash' becomes 'clean' (I've seen this before).
'come'+'clean'='COME CLEAN'
'and' is the link.
(Other definitions for come clean that I've seen before include "Make honest admission" , "Be completely honest" , "Own up (informal)" , "Admit" , "how you like your laundry to arrive?" .)