Possible Clues:

• Channel Islands firm demonstrating a tank
• Cold then I sit on hard bit of toilet
• Federal agents leaving monk in reservoir
• Tank hard to get on to islands
• Tank just over a hundred somewhere aft
• One demanding caution initially, at the front in tank
• Head for lavatory — is tension breaking into location of hadron collider?
• It's a bit hard to cut off the head of the water carrier