Underneath the Drowning Wench, there's a pair of ladies that are mugging a Roegadyn guy, and threatening to "cut off his wick" if he doesn't give them all his money. The wick, in this case, is his *****. They are threatening to castrate him unless he coughs up cash.
Well, let's be technical here, if we're talking castration and using candle euphemisms, the wick couldn't refer to the act itself, since "wick" obviously indicates the endpoint of a phallic object. The wick, as you say, is undoubtedly his *****, but the act is not the removal of his ********** and thus not castration.
I wonder whether anyone will realize that I'm not really arguing a serious point but actually seizing a great opportunity to unite two subjects too rarely discussed on these boards: literary devices and genital mutilation.