On Wed, 19 Dec 2007 17:33:39 CST, Chip wrote:

What are the easiest and most leak-proof ways to seal EDPM pond liner
for plumbing pipes?

You can actually seal a pipe EPDM junction by cutting the hole 1"
smaller than the pipe, so it makes a lip on the pond side. Some use a
clamp on the lip, others don't bother, so long as the lip is on the
water pressure side of the seal.
HARVYTHEKOI Has improved his with a collar:
http://www.koiphen.com/forums/showthread.php?t=51520

I hear you can get quite large EDPM sheets from roofing contractors.
What do they call it? and is it cheaper than from a pond supplier?

They called it roofing liner. (Some called it rubber roofing liner,
but it is my understanding, butyl rubber hasn't been available for a
long time.) I believe it came from the factory in 100 ft rolls and
the only width I bought was 25'. There may have been other widths
available then, but the last check revealed none of the local building
supply houses here carry EPDM liner. The advantage of buying locally
was the shipping cost.
--
Hal Middle Georgia, Zone 8
http://tinyurl.com/2fxzcb