I don't know what Detroit does, but you want to apply your final coat of urethane primer/sealer that is tinted close to what the finish color will be. That will give you better coverage with your base coat of color. The final primer/sealer coat is applied AFTER all your block sanding is done, and everything is tacked and washed with Dupont 3812 enamel reducer. Now you got a nice clean surface. The urethane primer/sealer and urethane top coat is applied "wet on wet". This means you let the primer/sealer flash (no sanding) and then spray your base coat of color right over it.
