Tucking is the practice of arranging and supporting external genitals between the legs, either by moving the penis and scrotum between the legs and buttocks, or pushing the testes up into their inguinal canals while arranging the penis between the legs. Either method is fine, although the sliding method is generally thought to be more comfortable. You can choose a gaff for tucking, or you can wear a gaff without a tuck. Both are valid!