I am trying to print out a network map using black/white hatching patterns, similar to Black/white hatching pattern fills in QGis but for Lines. Is there some trick I can use?
If you want to create a hatched line with a border you need to layer 3 linestyles (you can add them with the green "+" button). Your first (bottom) layer must be a simple black continuous line, set to a certain width (let's say 5).
If your lines have bends in them, be sure to set the connection-style to round (apologies, I do not know the correct English terms).
Your second layer needs to be a white continuous line that is placed on top of the black line to create the illusion of a black bordered line. This second layer needs to be a little narrower than the black one (4,25 for example).
Your third and top layer is the hatched pattern. For this you need to pick a simple vertical line symbol and give it an angle and also make sure the width reaches the "borders". With this grouped line symbol you can change the line width of the whole thing, no need to change each layer individually.