A Winkle is a teenyweeny shellfish that you prize out with a small pin. 'Winklepickers' (surprised no-one here has mentioned them yet) is an old fashioned term for a very pointy style of shoe popular in the 50's. Winkle is also a euphemism sometimes used by tots and their parents for the obvious as implied by MtheGM's song.. Maybe because it rhymes with 'tinkle'?

Never heard of wankle, though I've heard it lots of times without the 'le'