Like the previous poster said, it's not easy. It involves pretty much weaving a young chick (don't do this past one week of age) through the fingers of your left hand, stroking its belly with your right thumb until it poops, wiping the vent off, then using the thumb and index finger of your right hand to apply pressure to either side of the vent. The vent will protrude a little upon doing this. Male chicks' penises will be visible, looking like black dots about the size of a pinhead on the circle of the vent. If you're apprehensive about doing this, then don't. Holding a chick too tightly can cut off its air supply or injure it. You can always wait a few weeks until the males' saddle feathers start coming in, too...