One with common sense bottling hydrogen - to begin with engineer's not outsourced (2-5)

'not outsourced' is the definition.
(in-house means done within a company)

'one with common sense bottling hydrogen to begin with engineer's' is the wordplay.
'one with' indicates putting letters inside.
'common sense' becomes 'nous' (nous is a kind of common sense).
'bottling' is an insertion indicator (bottling is a kind of containing).
'to begin with' indicates taking the first letters.
'engineer's' becomes 'ie' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'hydrogen' is 'h'.
'nous' enclosing 'h' is 'nhous'.
'nhous' going within 'ie' is 'IN-HOUSE'.