The passive partner is on all fours. The active partner is behind them.
The passive partner is on their back with their legs up.
The Rusty trombone, in which a male is standing while the active partner is both performing anilingus from behind, generally from a kneeling position, while also masturbating the standing partner, thus somewhat resembling someone playing the trombone.
"Andrew's new chick loves playing 'the Rusty trombone' for him, whenever she get the chance!"