To add a an additional leader to an existing pipe size label, go to
Ribbon: DM Plumbing->Pipes-> 
Add Label Leader
Pulldown Menu: DM Plumbing->Pipes->Add Label Leader
You will be prompted to identify the pipe size label to which the leader is to be added.
Select pipe label:
You will then be prompted to identify the pipe to be labeled.
Select pipe to point to:
An additional leader will be inserted that points from the pipe size label to the selected pipe.