In order to properly clean the oil galleries, all the plugs must be removed. This is true whether you are beginning with an old block you've salvaged from the junkyard or a brand-new block. One that is easy to miss is the plug in the rear crossover gallery (it's just behind the rear main). Using a long rod, punch out each plug from the back side and then dispose of them. They'll be replaced with screw-in pipe plugs for better dependability.