My sisters and I learned to not be afraid of swimming in a rain barrel. It was the rain barrel at my grandparents' house in Saskatoon. During the summer my grandpa would fill it with warm water and I would spend an entire afternoon splashing around in this tiny barrel.
I don't remember clearly the first time I dunked my head, but I do remember that it was in that barrel and I felt so excited and empowered and brave, and I made sure my grandpa watched me do it again several times to prove I'd done it. After that, all I wanted to do was stand in the rain barrel all day and dunk my head, holding my breath for a few seconds, plugging my nose, over and over. I thought I had learned to swim.
Not entirely sure where the tube came into play... but I love this memory because it reminds me of how such a simple thing can be such an immense joy for a small child.