The simple trick is to draw an arc or three sided open polygon, then select "none" for fill in the attributes palette.
As a reminder, to set the default fill to "none", double click in some open space in the drawing (so nothing is selected), then set the fill to "none" before you start drawing all of those arcs or open polygons.
you can select a default line type and color in the same way.
Use this same method to return things to the way they were when you are finished.