A noble international charity organization you can call when you feel you gotta attend the call of nature but there is no toilet anywhere in sight.
Like the red cross sends an ambulance, the brown cross sends a truck with a toilet cabin.
This is a special case of a Big Kahuna, itself a large turd. When any portion of the turd sticks above the waterline, you have created a Brown Iceberg. Much like it's icy namesake, the vast majority of the Brown Iceberg lies below the surface. When turds have achieved this dangerous size, it will often not flush down the toilet, resulting in a Pooplug.