To select the block that is used as your leader, select:
DM Plumbing 
Customization Options Edit Standards List
The Design Master Plumbing Options dialog will appear.
The Pipe Leader Arrow Block setting will allow you to browse to any block and then set it as the arrowhead for Design Master Plumbing leaders. The default block, DM_DM-ARROWHEAD, looks like this on a drawing.
