The two bucket wash method comprises of using two separate buckets instead of one during the wash process. One bucket is used as the wash bucket and is filled with shampoo solution, the other is used as the rinse bucket and is filled with clean water. The reason that the two bucket method is used it that it greatly helps to reduce the transfer of small dirt and grit particles during washing which, if drawn over the surface of a cars paintwork can cause light scratches & swirl marks.
After a section of the car has been washed the idea is to then dip your wash implement into the rinse bucket and thoroughly clean it out. This allows any particles of dirt & grit that have been transferred from the car to be released into the rinse water. If used in conjunction with a grit guard (which the two bucket method should be) these particles can be thoroughly released and held safely and undisturbed at the bottom of the bucket.
After the rinsing stage the wash implement can then be dipped into the wash bucket to reload it with shampoo solution and because it has been rinsed out and released of any harmful particles it will not transfer them onto the surface of your cars paintwork when you continue washing.
A grit guard should also be used in the wash bucket as this further ensures that if there are any final stray particles that were not released into the rinse bucket then they will be safely captured under the guard and will not be picked back up by the wash implement.
After using the two bucket technique you can check its effectiveness by slowly emptying out the rinse bucket to see the dirt & grit particles that will have collected at the bottom underneath the grit guard. You can also check the wash bucket to compare it against the rinse bucket to see if you are sufficiently rinsing your wash implement out. The wash bucket should have little or no particles sitting at the bottom if you are correctly using the two bucket method.
Using the two bucket method in conjunction with grid guards, wash mitts & micro fibre towels instead of sponges & chamois leathers and a thorough pre foam/rinse, massively helps to reduce the potential for damage in the form of light scratches and swirl marks to be inflicted onto paintwork during the car cleaning process.