Preheat an outdoor grill to 400 degrees F (200 degrees C). Place turkey breast-side up in a roasting pan.
Put water in a large pot and bring to a boil. Add butter, seasoned salt, bouillon cubes, and black pepper to the pot; stir basting liquid well to combine.
Draw up 30 milliliters basting liquid in a marinade injector; inject throughout bird. Pour remaining liquid into bottom of roasting pan, cover with aluminum foil.
Bake turkey on the preheated grill, basting every 30 minutes, until no longer pink at the bone and the juices run clear, about 3 1/2 hours. An instant-read thermometer inserted into the thickest part of the thigh should read 165 degrees F (74 degrees C). Remove turkey from grill, keep covered, and allow to rest in a warm area 10 to 15 minutes before slicing.