Remove giblets from turkey; set aside for another use such as stock.
Rinse and drain turkey; pat dry.
Using a roasting pan large enough to accommodate turkey snugly, coat exterior of pan liberally with liquid detergent (this makes pan easier to clean).
Place turkey in pan.
Stud onion with cloves; place onion inside turkey.
Sprinkle outside of turkey with rosemary, thyme and sage, pressing herbs into skin of turkey.
Tie turkey legs together.
Pour about 1/2 inch (1 cm) water into pan.
Using 2 layers of regular foil or 1 layer of heavy duty foil, cover turkey right to edges of pan, sealing well.
Place pan on barbecue grill; cook over medium high heat 1-1/2 to 2 hours or until a meat thermometer inserted into the thickest part of the thigh registers 185F (85C).
If necessary, uncover turkey for last 10 minutes to brown skin evenly.
Remove from barbecue; let turkey stand, tented with foil, 15 minutes before carving.
If desired, make gravy from pan drippings.
Pour off excess fat from pan drippings.
On stove top or barbecue grill, place roasting pan over high heat; add 1 cup (250 ml) water.
Bring to boil, stirring to scrape up any brown bits from bottom of pan.
Season with salt and pepper to taste.