Job with firm installing supermarket's WC for example (6,8)

'wc for example' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'job with firm installing supermarket's' is the wordplay.
'job with' becomes 'post' (post is a kind of job. I am not sure about the 'with' bit.).
'firm' becomes 'strict' (firm can mean strict or severe).
'installing' is an insertion indicator (inserted letters are installed).
'supermarket' becomes 'Aldi' (Aldi is a supermarket chain).
'post'+'strict'='poststrict'
'poststrict' placed around 'aldi' is 'POSTAL DISTRICT'.

Can you help me to learn more?