Basically the gender reverse of the rusty trombone. That said, details matter. As the gentleman lovingly rims the fair maiden, he rubs his index finger along the moistened edges of her (insert preferred term) for her comfort. Next, slowly insert said finger in the aforementioned, while lovingly whistling the tune of her choice, hence creating a chorus of musical pleasure.
Ah girl, my man played me "patience" on the rusty slide-whistle last night, Guns-n-Roses never sounded of felt so good.