Ok guys, I 've been messing about with making a coupling out of the mini downpipe. What I have done is to cut two 12" sections of the down pipe. One section needs to have straight ends. You need to cut one of the ends of the other 12" section at an angle as it needs to slide into the other section. Heat the straingt cut 12" section very gently at one end. Wehn warm, slide the pointy end (you have just cut) of the other 12" section into it. Gently work it up the section reheating as necessary. Don't heat too much or it will tear.
Once you have expanded both ends of your 12" section, you have a coupling you can use for the longer 2m sections.