This is interesting. I knew people had to get rid of all leavened products in the house, but I thought they just threw them out...
For the Seder (Passover meal), it's common for the entire house to get the spic-n-span treatment to make sure there isn't even a crumb of leavened bread left anywhere. Even after the white tornado routine, some of the more stringent sects will cover the kitchen cabinets and counters with aluminum foil to make sure none of their Seder dishes come into contact with a speck of yeast that might have been missed.
But the truth is that the air everywhere is full of wild yeast spores. Sourdough bakers know this and some make their own wild sourdough starter just by leaving a container of water and flour (maybe with a bit of sugar or potato water) open, exposed and undisturbed for a few days. But the people who wrote these rules obviously weren't aware of that when they wrote them.
If this sort of thing interests you I would suggest you watch the 4-par Netflix series, "Unorthodox." It shows a lot of stuff that the typical Gentile probably would have realized, like a bride-to-be having her hair shorn before her wedding. And a wife reporting to the synagogue to have her ritual cleansing bath after her menstrual period ends, only after which may she resume intimate relations with her husband (because Jews have a lot of rules involving blood).