Daughter filling box in porter's room (5)
I believe the answer is:
lodge
'porter's room' is the definition.
'daughter filling box' is the wordplay.
'daughter' becomes 'd'.
'filling' is an insertion indicator.
'box' becomes 'loge' (synonyms).
'd' placed into 'loge' is 'LODGE'.
'in' acts as a link.
(Other definitions for lodge that I've seen before include "Deposit as to bank account" , "Deposit the house at the estate entrance?" , "Gatehouse; become fixed" , "Cottage at the entrance to the grounds of a big house" , "Masonic meeting place" .)