wrote:

I called True Value Hardware. They couldn't find this PBJ10041010001
plastic tubing/pipe.

TVH has changed their distribution system. My local store says this Endopoly
pipe is only stocked in one of their California warehouses :-) PT Industries
(1 800 44 ENDOT) and others also make cheaper irrigation pipe, eg $54.60
1/2"x400' and $71.60 3/4"x400' 100 psi pipes. US Plastics sells Cresline
3/4"x100' 100 psi pipe (item 24302) for $14.80, less 15% for 12 rolls.

Home Depot and Lowe's wanted similar 1$/foot for PEX tubing.

That's different.

...a heat conductance value for copper tubing?

I measured 30 Btu/h-F-ft^2 including still water on both sides. The water
films dominate the total resistance. IIRC, HDPE's thermal conductance is
about 2.6 Btu/h-F for a foot (vs 223 for copper), or 520 for a 0.06 inch
wall thickness, with no allowance for fouling.

I'm still calling around for reasonable quotes on a shotcrete cistern.

US Patent No. 3,933,628 "Method and Apparatus for the Anaerobic Digestion
of Decomposable Organic Materials," issued to inventor Frederick T. Varani
of Golden, CO on Jan 20, 1976, assigned to Bio-Gas of Colorado describes
a methane generator for a 100,000-cow feedlot, using 2 EPDM-rubber-lined
trenches, each 700' long x 80' wide x 40' deep. They cost $0.02/gallon,
including self-inflated solar covers and excavation.

Nick