Muireann,
you have described an attractive demonstration that could be used as a prompt for the children to engage with your topic.
With this tornado demo, the children might wonder about pouring smoothly – so you could give them a range of containers and water or other liquids to see how pouring creates glugs / noise / bubbles.
They might know about hot water bottles and how it is tricky to pour into a hot water bottle since the air has to come out.
In all inquiry activities the children should have a chance to share what they understand of the science, and make testable predictions. Some of these predictions may lead to a full-on, fair test activity, some might be quickly checked and then the children will move on.