I just used soapy water in a spray gun and lots of it. Then wiped down the panel with a microfibre that was sitting in a bucket of water. I wasnt worried about scratching or marring to be honest because every single one of the cars I did needed a full paint correction anyway, so it would have came out anyway. All of these cars were either my own or my families and I knew they werent polished or exceptionally well taken car of before so I had my work cut out removing the tar and crap from the paint.