Myth: Spiders found in bathtubs or sinks have come up through the drains from the sewers.
Fact: This myth goes together with the "coming in from the cold" one, and shows how very reluctant people are to confront the idea that the spiders in their house live there all the time. I don't know of even one case where a spider was actually shown to migrate into a house through plumbing; modern drains contain a liquid-filled sediment trap through which spiders cannot penetrate.
House spiders are thirsty creatures living in a very water-poor environment, and any that venture near a sink or tub with drops of water in it will try to reach the water, often by climbing down a wall. Once in the slick-sided porcelain basin, they are unable to climb back out unless a helpful human "lends them a hand."