To Place Pipe using Single-Line Mode

You can place Default Pipe, Flexible Pipe, Rectangular Duct, Round Duct, Oval Duct and Flexible Duct using Single-Line Mode.

Click Pipe on Plumbing ribbon.
The Placement Tab with the Place Component dialog opens.
Enable Single-Line Mode from the Flexible Options group on the ribbon.
Note: The Type, Item and Flex Length of Flexible Options on ribbon is enabled only for Round Duct, Flexible Duct and Pipe.
Select the Pipe Catalog Item from the drop-down list.

StraightPipe | Default Pipe

or
FlexPipe | Flexible Pipe
Select the Type from Flexible Options on ribbon under Placement Tab.
The Item on ribbon changes according to the Type selected.
Enter Diameter in the Place Component dialog and hit <enter>.
Enter a data point to place the origin of pipe followed by the second data point.
Enter a different Diameter value, hit <enter> and then give other data points.
Note: The Size option on ribbon in the Placement Options group should be disabled while placing a pipe with the new diameter value.

The Pipe is placed using the Single-Line Mode.