Thanks @PollyW!
Waw O_o That a really horrible story about flea infestation. My cats had fleas just once. I put some Advantage or Revolution on them once a month, for a couple of months to be sure, and the fleas were gone. I didn't need to wash, spray or do anything else. But I live in Canada, much more colder climate and they got infested from some other cat that my roommate brought from the shelter.