I need to join 2 pieces of breather pipe together.  I tried looking for a
plastic hose joiner at my local motor shoppe, and found some plastic ones
with ribs on (just what I wanted).  The only sizes they sell tho are 13mm &
8mm.  My pipe is approx 11mm.  I feel the 8mm will be too loose, and I've
tried the 13mm and cant ram it into the hose at all, too big.

I've got some copper piping which is just the right size.  I plan to cut a
length and fasten it with 2 jubilee clips.  Only thing I want to know is, is
there any chance the copper may 'deteriorate' and damage my engine?  The
pipe is breathing into the plenum chamber (it really is a breather and not a
vacuum line).  Is there any chance the copper piping could emit anything
that would damage the cat etc.........?