OK. I can't find the hot end right now but here is the pusher. It has to be a bowden pusher.

You can see the drum with only one pushing wheel in, I used the other for something else. In the other picture you can see the brass bit that rotates to push the filament. It will only push the filament that has the pushing wheel behind it, all the others stay where they are. To change colour you just rotate the drum until another wheel lines up. At the hot end I had a stainless pipe with the nozzle on attached to the end of the PTFE tube and the actual hot bit had a hole that the nozzle fitted into so that changing colours involved removing one nozzle/ptfe pipe and replacing it with another one so that the extruder nozzle stayed in the same place.

I had it working with 2 different filaments but lost interest at that point. I never automated the nozzle change because it is a pretty trivial thing to do so never bothered.

For whatever reason, I am unable to upload any pictures so I have stuck them here:

http://homepage.ntlworld.com/dknpowe...225_150548.jpg
http://homepage.ntlworld.com/dknpowe...225_150614.jpg