There's a laundry mat on Middle Street, but it isn't always open when you go for some reason. There are also places that will do your laundry for you.
I usually do my own by hand and hang to dry but that is one of the reasons that my panties ended up over at Lily's and my shirt in the hedge in front of the Mayan. Oops. Good wind in San Pedro so bring some good clothes pegs.