Most swirl marks are inflicted in the washing process. 2 buckets allow you to split dirty water and shampoo solution.
Bucket 1: Water & shampoo solution. Bucket 2: Grit Guard Insert and half filled with lukewarm water. Using bucket 1 to prime your wash mitt, wash an area of the car, then rinse your wash mitt in bucket 2 making sure to rub against the Grit Guard to dislodge any grit from your mitt. Then you are taking a clean mitt back into bucket 1 and repeating the cycle until the car is clean. NB. Work from top to bottom.