The co-ordinates for this cache will take you near the entrance to Shelob's Hallway.
You must then, like Frodo, find the courage to enter this dark, dank, and at times smelly, entrance and proceed approximately 200 paces in from the mouth. At this point you can summon up Galadriel's light to locate the 2ltr black-painted container; just put your lips together and blow. Update: Alas, as the Elves have sailed off into the West, thus has Galadriel's light now faded into darkness.
Important: GUMBOOTS ARE ESSENTIAL, as well as a torch. Unfortunately, over time Orcs have left their waste through here so be careful where you step at all times.
If you wish to proceed further, the hallway ends in Caversham, but that end is even wetter!