To connect a new pipe to a pipe symbol, go to
Ribbon: DM Plumbing->Pipe Symbols-> 
Connect Pipe to Pipe Symbol
Pulldown Menu: DM Plumbing->Pipe Symbols->Connect Pipe to Pipe Symbol
You will be prompted to identify the pipe symbol to which a new pipe is to be connected.
Select pipe symbol near point to connect pipe to:
You will then be prompted to insert pipes on the drawing.
Specify next point for forward pipe or [Set pipe information/Vertical/start New run]:
See the Insert Pipe section for more information about inserting pipes.