Spank to find shallow water? (6,6)

I believe the answer is:

strike bottom

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'shallow water?' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'spank to find' is the wordplay.
'spank' becomes 'bottom' (I am not sure about this - if you are sure you should believe this answer much more).
'to' means one lot of letters go next to another (I've seen this in other clues).
'find' becomes 'strike' (striking is a kind of finding).
'bottom' put after 'strike' is 'STRIKE BOTTOM'.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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