If I have heavy dusting from multiple polishings, I go ahead and wash the car before the final light polishing and wax/sealant. I go a little heavy on the soap for the added lubrication. The loss of oils from the heavy soap use is replaced by the final light polishing (which leaves no dust being a Megs pure polish). Follow this with the sealant, and a wipe down of the exterior trim with a protectant, and I'm done.