Hey there,

To create a pipe:

1. Place down a Pipe Entrance Trigger and a Pipe Exit from the Special category.
   
2. Select both of these, right click to open the context menu and click Create Pipe Link.
   
3. There now should be a link between the pipe entrance and exit.
   
4. Select the link and click the Open Properties Window button on the right of the transform options bar to edit the pipe's properties.

You can also select multiple pipe entrances and exits and they will all be linked together. Pipe entrances that have multiple exits will choose an exit randomly.

-Kevin