Better than a a Rusty Trombone, it's an enhanced Deep Throat.
1) To perform fellatio (dick-sucking) similar to Deep Throat, where the entire penis up to and including some of the scrotum penetrates into the performer's throat well past the tooth line (usually causing repeated gag reflex to beginners), and then to trigger orgasm, full insertion of finger(s) (the number of fingers (+1 for penis determines the name of the act, i.e., two fingers would be a Triple Deep) into performee's ass sets off the mighty, uncontrollable finale'. (Sometimes variations including gentle scrotum-sucking by performer, enhanced by alternating stuffing of a nut into mouth opening not more than what would cause a breathing restriction is said to enhance the eroticism level for both participants);
"Dude, my #1 squeeze insisted she Double Deep me last night. It was awesome,...bigtime. Way better that her best Rusty Trombone has ever been! Whoa. I still tingle!"