On Mon, 2 Jul 2007 21:44:14 CST, "Bill Stock"
wrote:

Did you leave any slack in the liner around the drain?

No, in fact because there was about a 1 in 4 foot drop/taper to the
center, it was sort of a stress point, since it was bolted, glued into
the liner at that point and pulled, gently, from the sides. I
couldn't work all the wrinkles out because of the tapered bottom and
wouldn't allow more than a couple inches difference if I were doing it
again. I can't see the liner needing any slack. I used Permalon as a
liner, but rubber will give a bit and .040 should work fine as well.

I'll have to work out the kinks once I actually lay my hands on one. I don't
plan to dig up the existing pond until I'm closer to getting the piping
done. I bored the concrete on the weekend, but did not start the
'tunneling'. Pesky rennovations saved me from the 'good stuff'. :-)

The reason I said I would take my time planning the concrete, the
instructions with my bottom drain were a bit vague to me, so I
calculated for myself how much space I wanted between the dome
perimeter and the liner when it was set. The tapered bottom that I
wanted made it more difficult to make measurements under the dome, but
I was pleased when I finished. A year or so later I noticed fry in
the filter barrels and found they could pass freely under the dome and
when I checked the dome clearance between it's perimeter and the liner
it had moved enough to allow the opening to increase to what looks
like more than 1/2 inch maybe 5/8. That wasn't a serious problem,
just wasn't what I expected. With concrete and a mockup of the drain
I could have formed exactly what I wanted it to be and it would be
exactly as I formed it years later. The instructions warned me to use
cement, but I had plenty of confidence in Georgia clay.

Regards,

Hal