Summarize:

Another way to tell the sex of a guinea fowl is to examine the vent, which is the genital area of a bird that controls the elimination of bodily fluids. To perform vent sexing, use one of your hands to turn the guinea fowl upside down and push its tail towards its head. Consider having a friend help you with the procedure.  It would help to be seated and rest the guinea fowl's back along the length of your leg. Vent sexing can be difficult to perform and may injure a bird. If you are not comfortable performing the procedure, have a bird expert do so. Vent sexing is usually performed in keets that are at least a few weeks old. The cloaca is the circular opening where reproductive, urinary, and digestive fluids exit a bird’s body. With your other hand (or the hand of your friend), place an index finger and thumb on either side of the vent. Gently separate those fingers to stretch and push out the cloaca. Use gentle, yet firm pressure when exposing the cloaca. Typically, it is very difficult to differentiate between the sexual organs of male and female birds. A male guinea fowl’s phallus is longer and thicker than that of a female guinea fowl. The phallus becomes more distinguishable between the sexes at around 8 weeks of age.
Turn the guinea fowl upside down. Expose the cloaca. Examine the phallus.