A sexual position encountered during a threesome or Menage a Trois. Characterized by one male performing oral sex on a female as she is lies declined (downhill) while she simultaneously performs oral sex on male #2, who is in fact lying on his back on the floor.
1) Yo homie, I heard that Ralph was doing a Downhill Double Dip the other night. He said it was crazy!
2) Did you see that chick when she was Downhill Double Dippin'?! She is very talented.