1. The Aravos used in the special service were from a place near Yerushalayim called Motza.
2. As part of the Aravah service, the Shofar was blown every day of Sukos, and the Mizbe'ach was encircled once.
3. Rebbi Yochanan ben Berokah: On the seventh day of Sukos, palm branches were brought to the Beis ha'Mikdash.
4. After these customs (#1-3) were performed, the adults would throw down the Lulavim of the children and eat their Esrogim.
5. One who concludes the festival with a festive meal is considered as though he built a Mizbe'ach and offered a Korban.
A BIT MORE
1. These very long Aravos were collected and then put on the side of the Mizbe'ach. The tops of these Aravos would curl over the top of the Mizbe'ach.
2. Tana Kama: They would say while circling, "Ana Hashem Hoshi'ah Na, Ana Hashem Hatzlichah Na." Rebbi Yehudah: They would say while circling, "Ani v'Ho Hoshi'ah Na."
3. He says that they would beat these palm branches on the floor next to the Mizbe'ach. They called this day, "Yom Chibut Chariyos" -- "The day of the beating of the palm branches."
4. This was permitted without even asking the children's permission, in order to show the happiness of the day.
5. Some say that this refers to the festival itself. Others say that this refers to making a festive meal on the day after the festival (commonly known as "Isru Chag").