The pin behavior will not set the platform to the pipe's position and angle, it will only keep it there if you move or rotate the pipe. Consider using Set position to another object on the platform to set it to an image location on the pipe, and then you need to set the angle to the pipe's angle.
You might want to place a pipe in a container with the platform. So that any time the pipe is created or destroyed the corresponding platform will also be created or destroyed. (Select the pipe in the projects panel, and then in the properties panel under Container click on create. In the window that pops up select the platform.)
You might want to consider placing all of your pipes in a family. That way any behaviors, actions, etc... can be applied to the family as a whole. You can still apply things uniquely to elements of a family when needed.
You might want to consider reducing some of your file sizes. You make nice artwork, but I think things will become unruly as you add more layouts.
Have you thought about how you are going to have Slimy go up a pipe? Or decide to go up a pipe at a T intersection? (Look out, here comes another you might) You might want to think about these things before you go too far down your current path.