Place the brisket fat cap down in your roaster or in the bottom of a cast iron dutch oven or baking pan with a lid.
Sprinkle on the salt and pepper until the brisket is well coated. Rub the seasonings in. Flip it over (fat cap up) and sprinkle on salt and pepper, then rub in. Leave the brisket fat cap up for cooking.
Peel your garlic cloves, then chop each one in half. Using a large, sharp knife, stab the knife about 3/4 inches into the fat cap. With the knife still inserted to keep the hole open, slide a garlic clove half into the hole. Remove the knife, and shove the garlic clove in until it's barely visible or has disappeared.
Though the above image is of chuck roasts, not brisket, you'll insert garlic into the brisket using the same technique.
Repeat inserting the garlic until all the garlic cloves have been inserted into the roast and distributed evenly over the surface of the roast.
Place a few pineapple chunks on top of the roast (4-8, depending on roast size). Distribute the rest of the chunks in the pan around the roast.
Add water to the pan until there is about 1 1/2 inches in the bottom of the pan.
If using a roaster: Turn the roaster to 400 degrees F and roast in the roasting pan, covered, for 45 minutes (30 for a small roast) to allow the fat cap to begin to melt down. After the 45 minutes, reduce heat to 175 degrees and cook at this temperature, covered, for 8-12 hours (overnight is fine). Maintain about 1 inch of water in the bottom of the pan at all times (or about halfway up the side of the roast, never above the surface of the roast). If you're cooking overnight, bring water level to about 1 1/2 inches before going to bed. When done, remove from heat, slice the roast against the grain, and serve sitting in the juices in the roasting pan.
If using a dutch oven: Place the uncovered dutch oven on the center rack of a preheated 400 degree F oven. Cook for 30-40 minutes (30 for small roast) until fat cap has begun to brown. Then cover the dutch oven and reduce heat to 175 degrees F. Cook for 8-12 hours until meat is tender before slicing against the grain and serving with roasting pan juices.
Note: you can also use some of the roasting juices to make a nice gravy. Just ladle into a saucepan and bring to boil. Once boiling, stir 1 tablespoon cornstarch with 2 tablespoons cold water in a cup. Pour the cornstarch and water into the boiling mixture and immediately stir. Stir continuously until the mix returns to a boil, then remove from heat.