But when we tried to run the Ethernet cable from the roof to the basement, we discovered that the conduit makes 3 90-degree turns and one 45-degree turn, and it was not at all clear how one pushes a cable through such a maze.
So of course we turned first to the internet. I typed in a totally natural language question into Google (which I find these days is increasingly the best method): something like “how do you thread a cable through a long conduit with 90 degree angles.” The first post that came up was a thread from some list titled Threading fiber through a long conduit. This thread reported no good luck, but it had the kernel of an idea: a vacuum cleaner.
So we took a bit of foam, tied it to the end of a roll of kite string, and connected a small Shop-Vac at the other end of the conduit (which is at least 50 feet long). Bingo. The key, it seems, is to have a big but light obstruction, and google at hand.