How did Dobby iron his hands when he shouldn't have been allowed near clothes?

During Chamber of Secrets, Dobby is forced to iron his hands as a punishment for betraying the Malfoys' secrets to Harry. How did he do that? Wouldn't he have been able to free himself if he was given tasks which involved clothes?

Also, who (in story - in reality it was obviously JKR) would have come up with the house-elf clothes rule in the first place? I'd have thought that laundry would be one of the main tasks you'd want a house-elf helping with! Even though magic would make washing easier than it would be without, I'd imagine there'd still be some prestige in not having to do it yourself.