When the Flex Duct tool is selected, the Place Flex Duct tab provides the following options for placing piping:
Tag on Placement: applies the default annotation tag to a duct segment when it is placed in the view.
Automatically Connect: lets you automatically connect to the snaps on a component when starting or ending a flex duct segment. This is useful for connecting segments at different elevations. However, when drawing flex duct along the same path as another duct at a different offset, clear Automatically Connect to avoid making an unintentional connection.