Rowan -

I think the egg cartons on the wall may be at least partly mythic.

When my son's "rock band" played in a small room that I'd enclosed solidly in the basement, with egg cartons on all four walls and ceiling, and with limp carpet suspended in front of the egg cartons, with all doors and windows shut and where necessary provided with styrofoam plugs at least 5 inches thick
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we still got complaints from neighbors up to 3 blocks away.

I don't think anyone could have detected an echo of any sort when they played - but of course they weren't recording.

The use of ABS for sewer/drain pipe in the US is apparently a matter of economics. The ABS is usually at least a bit cheaper than PVC of the same bore, and the ABS usually has a slightly - to significantly - thicker wall. ABS generally is used only for drain lines inside the structure, with clay, concrete, or cast iron still being preferred for "public sewers" (laterals and mains) so far as I know.

Some use is made of "plastic" conduit for wiring, but the stuff commonly found in the shops is a slightly different composition than the PVC, and generally is grey in color rather than white. What I've seen of it appears to be a "filled" plastic, probably for rigidity and heat resistance. It appears to be a thermoset rather than thermoplastic material like PVC, but that could be due to a powder filler. A vague recollection is that I've heard it called "PVA," possibly a "polyvinylacetate," although I can't give any assurance of accuracy on the material.

In many usages in the US, metal tubing is required for electrical conduit, both for conductivity and for heat resistance. Mostly thin-walled steel tube is used (with a terne plate coating?), but there is some usage of aluminum. There are few truly "national" standards, although there are "guidelines," so usage varies a lot by locality within the US.

John