Combine the liqueur, tequila, orange juice, lime juice and grapefruit juice in a large pitcher and mix well. Chill, covered, in the refrigerator.
For guests who prefer salt, rub the rims of your margarita glasses with lime wedges and dip in margarita salt. Fill the glasses with ice. Shake the chilled margarita mixture in a cocktail shaker filled with ice and strain into the prepared glasses. Garnish each serving with orange, lime and/or grapefruit slices.