sharkie is right about the first 2 bucket method. That is the one most autopians use, one soapy bucket, one clean water bucket. First hose the panel, then dunk in soapy bucket (not all the way to the bottom so you wont pick up dirt that fell out of the solution) and wipe the panel in a back and forth motion (direction of airflow). Then dunk the mitt in the clean water and rinse off all the dirt (do this VERY often if the car is very dirty). This highly reduces the amount of swirls that you will get later. BTW I used to use a sheepskin mitt on my ML, thats how I got all my swirl marks . Wish I knew about autopia back then.

edit: after you finish getting the swirls out I would apply a polymer sealant like klasse. This will help protect from future marring and provide additional UV protection. The reason I suggest klasse for you is because it looks great on black and you can continue to use souveran as a topper, unlike zaino . check the pictures of my black ML on the member pictures forum

AlBoston's black ML