Thought of a few today,
1. A tool to tell us where to drill through a joist so that it is straight
2. A clip that holds pipe up while soldering
3. A tool to stop movement on pipes whilst soldering
4. a tool to push pipes so that they dont pull out when soldering
5. some way of cleaning pipes when you take them apart so when you put a different fitting on it is easy to put back on.
6. an app with all the most important regulations on it, cutting joists etc
7. a toolbox that tells you when you are out of flux, glue, solder, wire wool etc
8. a gas bottle that tells you when you are down to 1/4 full