I know professional installers who use a single bucket (I use a divided bucket) with no problems. Optimum does not recommend one method over another (unless giving personal opinions). My drying towel collects some minimal dirt, usually around corners/nooks/crannies where the BRS doesn't make as much contact. Again, too much dirt on your drying towel is a bad sign. As to Setec's point of accepting some marring, I have a Coated car that has not marred at all and an uncoated car that has minimal marring/micro marring - same dude washing, same products, same procedures. Sales pitch for Coating?