Both are correct, though "fregar" is mostly for when you rub something forcefully against another thing. The best way to say it would be "lavar" (http://lema.rae.es/drae/?val=lavar) because even though "fregar" has a similar meaning (http://lema.rae.es/drae/?val=fregar) it's also colloquially used as a term to mean "annoy" or "to cause harm or prejudice to someone",

Yea, lavar is more common. I've heard the word "fregar" not to much times and in the times that i've heard it I think the same as if the had told me "lavar"