With a lot of effort, Lisa got the 10/3 electrical wire (orange) through the 3/4-inch conduit (gray). She then routed it along the under-floor beams (putting in brackets to hold it in place) and pushed it up through the hole in the floor.
Lisa was very happy when she came out from under the house, because she says the under-house electrical work is now done. She doesn't have to go back down there anymore. There's about 2m of conduit and wire coiled up in the bathroom floor awaiting her installing the cut-off box for the hot water heater.
We went to Lowe's this evening and bought a 20A circuit breaker to replace the 60A breaker that came with the cut-off box. The 10/3 line will be connected to a 30A breaker at the main box, but inasmuch as Lisa has specified the 3000W/240V (thus 12.5A) heating element for the water heater, she wanted to put the smaller breaker on the cut-off box. Everything is just a little over-engineered and with a lot of leeway, which is just how she likes it.
Once she has finished building the base for the water heater and installing the cut-off box, we can call our plumber and say, "Ready when you are."