"Chris" wrote:

I'm about to start excavating a pond 4' deep with a 55 gal drum filter
(drums 3' high; jj's design). One nagging doubt I have is about the
pipe from the bottom drain to the filter. It'll have to run uphill at
least 1.5' in order to enter the filter. Seems to me that with enough
flow I shouldn't have problems with the pipe clogging, but I'd feel
better about it if the pipe ran down rather than up.

Have you considered using a skimmer output rather than a bottom drain.
Bottom drain ponds have more trouble because of sediment, even when they
don't drain uphill.
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18,000 gallon (17'x 47'x 2-4') lily pond garden in Zone 6
Cheers, Steve Henning in Reading, PA USA