Rinse the spinach well in cold water to make sure it's very clean. Spin it dry in a salad spinner, leaving just a little water clinging to the leaves. In a very large pot, heat the olive oil and sauté the garlic over medium heat for about 1 minute, but not until it's browned. Add all the spinach, the salt, and pepper to the pot, toss it with the garlic and oil, cover the pot, and cook it for 2 minutes. Uncover the pot, turn the heat on high, and cook the spinach for another minute, stirring with a wooden spoon, until all the spinach is wilted. Serve hot.