Here is how I've set mine up.
I use a Swivel. This way I either clip a roller troller to the swivel or the tag line, depending on what's happening.
this is my tag line:
And this is how it's made up. Both ends have a clip on. The one is for clipping to the swivel on the outrigger line and the other for clipping the elastic band. The Bung it pulled over the knot shown below to keep it in place and stop it from moving up and down. It is on the end that you fit the elastic. This way, when I remove the tag line, the bung comes with it as it is unnecessary for normal roller troller use.
The Bung has 2 main functions.
1 - When the line goes, the slide slides down and rests on the bung keeping the tag line at hand and out the way.
2 - It creates a little resistance. When the elastic breaks, it stops the tag line from "flicking" back which sometimes causes the tag line to flick over the outrigger.