5mm pipe is the rear window washer pipe. the tank breather pipe goes parallel with the bigger filler pipe, then goes through a chassis hole and to the top of the tank. tis a tank-out type job to access. soft rubber tended to kink and so restrict venting & cause pump to click prematurely
check my blog #111 for details/pics on it
http://www.micra.org.uk/threads/35251-PollyMobiles-Rebuild/page3
