"Iain Miller" writes:

I was planning on having an external filter at the same level as the pond so
that water will flow into it & then putting some kind of pump on the clean
side - the logic being that it would be better to just suck the rubbish out
of the pond into the filter (possibly into some kind of catchment chamber
first) rather than "liquidizing" it through a pump before it gets to the
filter.

Plus the junk can clog the pump or at least make cleaning the pump
screen a daily task..

Another solution I was advised to look at was to have a bottom drain that
just went to a waste pipe so that periodically I could just open it & suck
the rubbish from the bottom of the pond straight to waste. Then to mount the
outlet for the filter about halfway up the side of the pond. The other
question related to this is as to whether its worth putting in a surface
skimmer or not.

The area my pond will go in naturally restricts the size it can be (we are
only talking about 1000 gallons or so).

Make it deeper? I'm shooting for 5 feet for my rebuilt one (3 feet deep now).

However, there is a redundant (and
non visible) area close by where I was considering placing some larg-ish
water tanks (with lids on) - the idea being to pump water out from the
filter upto these which would then overflow back to the pond. The idea of is
to increase the overall water volume of the system.

Use them as your filter. First one a settling tank, second one with
bio filter media. I'm digging something similar right now :-)