The "rusty venture" is the name of a fictional sex act. The act is named after one of the main characters of the Adult Swim show "The Venture Bros.," Dr. Thaddeus S. "Rusty" Venture. It is referenced throughout season 4, episode 16.
The definition of the "rusty venture" is disputed among characters within the show:
1. (gay) Running one's finger around a man's anus, while simultaneously masturbating him, and making him release into his own face.
2. (gay) Two men performing a "69," filling each other's mouths with semen, then turning around and blowing the semen into each other's buttcracks.
3. (neutral) Placing one's penis into one end of a scuba snorkel, and putting the other end of the snorkel into one's own anus; the tube portion is then used simultaneously for masturbation and anal insertion, until one releases and allows semen to flow through the snorkel into one's own anus.
4. (gay) (definition unclear until uncut DVD is released, or someone with a better imagination comes along)
5. (straight) a) The "rusty" portion consists of a man having anal sex with a constipated woman, allowing her to defecate on his penis; when the man orgasms, he releases a mixture of semen and feces onto the woman's back. b) The "venture" portion consists of the man eating the "rusty" portion's resultant mixture from the woman's back without the assistance of hands (or implied other utensils).
6. (neutral) The result of masturbating to the point of one's penis becoming red and sore.
Whore: "I'm gonna give you a rusty venture!"
Brock: "Don't believe the hype. A rusty venture is the name for when you jerk off so much your dick gets all red 'n sore."