Saw brute getting into passenger boat

I believe the answer is:

waterbus

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'boat' is the definition.
(I know this)

'saw brute getting into passenger' is the wordplay.
'saw brute' anagrams to 'WATER BUS'.
But, I'm not clear how this is indicated.

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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