Thanks. Wont that act as an overflow. I guess thats fine if you leave
run for the water to run away but if you connect all the conduit back
to the socket then you risk water running back to it during heavy
rain.

Just a few further thoughts.
We've always been told to install overflows beneath the edging slabs or
stones. This is to kep the level constant and keep the water from coming up
over the edging when the pond fills with rain.
This is not for aesthetic reasons, but because of the power of melting ice.
The pond sides should always slope outwards so that any ice formed cannot
exert sideways pressure when it melts. (Ice EXPANDS when it melts, which is
why it can burst pipes)
If the water level rises to the capping stones then melting ice is trapped
and can loosen the mortar and make your pond potentially unsafe.
We have five ponds, all but two fitted with overflows. (The other two have
waterfalls and can't over-fill)