At Heathrow Airport. Airplanes - Civilian - Static Display - Large jets Links: www.simulation-ters.co.uk By: kjfitz
Looks like it gets towed elsewhere for setting on fire. And they definitely do use it for external fires not just internal fires.
http://aviation-safety.net/photos/displayphoto.php?id=990050&vnr=1&kind=F
http://aviation-safety.net/photos/displayphoto.php?id=990074&vnr=1&kind=F