The Break Pipe command will break a single pipe into two pipes.
To break a pipe, go to
Ribbon: DM Plumbing->Pipes-> 
Break Pipe
Pulldown Menu: DM Plumbing->Pipes->Break Pipe
You will be prompted to specify the location of the break on the pipe centerline.
Select pipe at break point:
The pipe will be broken into two pipes. Both pipes will point in the same direction as the original pipe.