Do carriers wash aircraft?

[NickN]

Something I have ALWAYS wondered about...... Do carriers run their aircraft through the ol' drive-thru every now and again? Or do they rely on the "natural elements" to keep the aircraft exterior clean?

At altitude one would assume grit and dirt would become frozen and in conjunction with the high velocity airstream passing over the aircraft body would be "blown" off. But I wonder if that means an entire clean or do the aircraft still need a Wash'n'Wax every now and again.