They're both right, it sort of depends if you want to do the job or to
do it properly.
The pipe is called ducting and your kitchen company probably sell it in
2 metre lengths. It can be rigid or flexible. You'll need to fix it
to the fan and the outlet so you'll probably want 2 jubilee clips or
you could just use some gaffer tape. A non-return (or flap) valve
isn't essential but it will stop outside air being blown in when the
wind's in the wrong direction. You'll probably also want an outlet
grill as a bare ended pipe isn't very pretty and is a bit of an
invitation to the local wildlife.

Try QVS on Coldhams Road. Not only have they got all this stuff
cheaply but their catalogue has got pictures. Come to think of it
their catalogue is online too at www.qvsdirect.co.uk