Gravel for your duck Share definition Flag the theory that, as a duck needs gravel to eat and digest its food, a man needs sex to live. "Man, I'm taking you to the bar tonight. You need to get some gravel for your duck" Gravel for your duck by old man dan March 1, 2008 0 0 Get merch Get the Gravel for your duck mug. Buy Now — $32.95 See more merch