How often is the exterior of airliners cleaned? Do airlines such as American Airlines or Emirates clean their planes regularly?

If so, how regularly? After every flight or at scheduled maintenance points?

How long does this activity take? Do they apply any wax or polishing to the plane?

I am interested in the general upkeep of the exterior of the plane and what major commercial airlines do to upkeep their planes.
According to Lufthansa Technik, with the new cleaning agents, once every 6 months.


  Until just a few years ago, wide-bodied aircraft had to be washed four times a year with foam and up to 13,000 liters of water. Today, thanks to newer cleaning agents, a resource-friendly dry wash every six months is enough.


It takes between 8 and 24 hours to wash or dry wash an airliner.