Two bucket method is basically one bucket full of shampoo mix and the other is clean water. Every time you shampoo the car, dip your mitt in the clean water and shampoo again. Get a grit guard as well, this is placed at the bottom of your bucket so you rub your mitt over it. It releases any grit and holds it at the bottom of the bucket. If you want to get serious about car cleaning, you then need to look at claying, polishes, glazes, sealants, waxes, microfibre clothes, drying towels etc.