I'm looking to put up a polytunnel in part of the garden that,
although less than 10m from the cottage, I cannot get water to without
significant engineering,

I can see two options at the moment and would be interested in any
comments.

I can tap off the mains feed to the water tank in the attic, run an
MDPE pipe over the wall head, down the 3m high wall, put a suitable
drain point at its foot and then under ground to the polytunnel.

The second is the one I would like to try to implement but cannot see
my way round some of the complications. The cottage is nearly 60ft
long and requires a new soakaway for the rones on that side of the
roof anyway (no mains drainage) - logic says that there would be more
than enough water, but I am having difficulties seeing how the storage
and watering in the tunnel would work and also how to get rid of the
excess water during the winter (and summers in Scotland!).

Thanks for any assistance

Rob