Shape of toilet turning round first (4)

I believe the answer is:

oval

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'shape' is the definition.
(oval is a kind of shape)

'of toilet turning round first' is the wordplay.
'of' becomes 'o'.
'toilet turning' becomes 'vl' (I am not sure about this - if you are sure you should believe this answer much more).
'round' means one lot of letters goes inside another.
'first' becomes 'a'.
'vl' enclosing 'a' is 'val'.
'o'+'val'='OVAL'

Can you help me to learn more?

(Other definitions for oval that I've seen before include "Stretched circle?" , "6D 5A [TUBE STATION]" , "sports ground" , "Elliptical figure" , "Like eggs" .)

I've seen this clue in The Guardian.

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