During large caliber stream operations, what should be done when taking up?

The correct action during large caliber stream operations when taking up is to open drains on the main waterway while the boom is elevated. This process ensures that any residual water in the system is properly drained, preventing back pressure and potential hazards or damage. It also allows for a smoother transition back to less intensive operations, as it helps clear any water that may still be present in the lines.

When the boom is elevated, it ensures that the large caliber stream remains effective while the drainage takes place. This practice enhances safety by minimizing water accumulation that could lead to unwanted pressure builds within the system.

The other options might seem reasonable in a different context, but they do not directly address the specific needs and safety protocols during the take-up phase of large caliber stream operations.