When fitting pole elastic, the bung end is done before threading the elastic through the sections and attaching the connector. There are all manner of bungs on the market and they all work, but I like ones which allow you to tension the elastic and in particular I like the Vespe bungs shows in the sequence below. It cuts out the need for a tag end of line at the bottom because it comes with a special attachment to remove the bung, and there’s also an invaluable fitting to allow you to alter the tension. If you use a bung like this, wind two or three turns onto the tensioner when you set the elastic up. Then, if you set the elastic up too tight (which is easily done) you can release a turn or two, and if it’s too loose you can wind another turn on.
Gareth Purnell, Improve Your Coarse Fishing

1.
Pick a suitable bung and mark where it jams in the section. For most fishing situations for elastics up to No8, you won't go far wrong fitting the elastic through the top two sections of your pole.

2.
Now cut through the bung just above this mark with a saw, knife or Stanley knife so the bung will fit inside the pole.

3.
Take your elastic and attach the bung with a double overhand loop. If you have trouble getting the elastic through the hole, cut it at an angle to create a point.

4.
It's good practive to double up the elastic for about eight inches above the bung. If you hook a fish big enough to bottom out the elastic, this gives you a short length of elastic effectively twice the strength of your original elastic, and this can be enough to turn a fish which would otherwise break you.

5.
Dampen the knot, tighten it, and then trim off the loose end.

6.
With this bung I now wind on about three turns of elastic which gives me a bit of room for mistakes when I come to attach the connector.

7.
With many bungs you will need to attach a length of thick line below so that you can remove it quickly and easily. Many's the angler who has forgotten to do this and ended up with a bung inside a pole section which he can't remove..