Get your Agent's agility up to level 5 so you have the Wingsuit and then spawn at the Agency tower. Move to the right and look for a large cylindrical pipe which is directly in front of the Agency holding pen building. This cylindrical pipe will be very tall and is the only one that has an opening at the top. Jump down and use the Wingsuit's glide ability to slow your descent as it is a long drop to the bottom. When you reach the bottom you will find yourself in a small cave where there is a very large toilet, rubber duckies and beach balls.
Added by: Sanzano Jul 9th 2010, ID#5991