I have the sea scout. It's great. However, I've got a couple questions about it. It came with a replacement nose plug. How are you supposed to change it? It doesn't say anything about it in the instructions. Also, what does that screw on the bottom of the sub do? I unscrewed it and it looks like it holds nothing together. I was wondering if it was maybe a place to add water to change its ballast. If anyone has ideas or answers that would be great! Thanks