[Bill Douglas]

What's worked for me a few times is to get a wire coat hanger and make it into a straight length with a 10mm hook on the end. Shove it down the pipe where you have taken the s-trap off and when you meet some resitance twist it as you push it then pull it out - hopefully pulling out the blockage with the hook. It's bendy enough to make it around corners and if it gets stuck you can always forcefully yank it back out.