To drain the oyster, place a strainer or small colander over a 4 or 8 cup glass measuring cup. Place the oysters in the strainer and set in the refrigerator. When ready to use the juice, empty the measuring cup into another vessel and add enough stock to make 5 cups of liquid. Place the strainer with the oysters over the original measuring cup and return to the refrigerator, they will continue to drain and you should add that extra oyster liquid into the bisque when adding the oysters.
Be careful adding salt. Many commercial creole seasonings contain salt and the oysters and oyster juice could be salty. Taste the bisque after the oysters have simmered for 10 minutes and add kosher salt to your liking.