While it's a must in some countries, this restriction does not apply to Egypt. No, you don't have to cover your ankles, or yourself from head to toe.
What are public toilets like in Egypt?
Toilets and Facilities:Public toilets, when they can be found, are usually squat-holes in the floor with footrests on either or if you are lucky western style toilets. All public toilets come with an obligatory usage free of 1-2LE irrespective of standard of hygiene.