Brainerd Helicopters out of Florida operate two S-70s on US Forest Service CWN contracts. They don't have tanks fitted as far as I know. Everytime I've worked with them, they have been using a Bambi bucket/long line with a video camera/cockpit screen for bucket work.
The story I was told, as near as I can remember, is that one of the aircraft came from the Sultan of Brunei (or one of his daughters) and the other was came from the Queen of England (via an engine manufacturer who was using it to test their engines for a possible engine alternative)