Gangster in Wales swimming from ocean container? (7)

I believe the answer is:

seawall

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'ocean container?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

'gangster in wales swimming' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'in' means one lot of letters goes inside another.
'swimming' is an anagram indicator.
'wales' anagrammed gives 'seawl'.
'al' placed into 'seawl' is 'SEAWALL'.

'from' acts as a link.

Can you help me to learn more?

(Another definition for seawall that I've seen is " sea defence".)

I've seen this clue in The Irish Times.

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