Handy sailor outside starts to go east in pyjamas (9)

'pyjamas' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'handy sailor outside starts to go east' is the wordplay.
'handy' becomes 'nigh' (I can't justify this - if you can you should give a lot more credence to this answer).
'sailor' becomes 'tar' (slang term for a sailor).
'outside' means one lot of letters goes inside another.
'starts to' says to take the initial letters.
The first letters of 'go east' is 'ge'.
'tar' placed around 'ge' is 'tgear'.
'nigh'+'tgear'='NIGHTGEAR'

'in' acts as a link.

Can you help me to learn more?