If using a stock pot or other container than a bag to brine the bird make sure it is fully submerged in the liquid by placing a plate, pot lid or other suitable weight on it and cover.
Wrap the peppercorns and allspice in some cheese cloth or use a tea infuser. If not you will have to pick the corms off the bird.
Don’t over brine the bird! If it sits longer than 24 hours it will not be the end of the world but the texture will start to degrade the longer it sits.
All you really need to brine a bird is saltwater. All the rest is just flavor so feel free to experiment.
Make sure you use unsalted butter the turkey has plenty!