You don't have to use a pressure washer, but a bristle brush with plastic bristles will help dislodge stuff you might not even see. Get you some of those brushes @kursplat linked to clean your oil galleys out. If you're gonna grind that casting flash out, do that before you wash it. Use those Summit brushes in the oil holes thru your crank journals also, to get the metal shavings out of those holes. I'd say the machine shop dipped the block and shot blasted it first to get it clean, then did the machine work. The fluid they use while boring/grinding will carry the iron dust into places to hide it until the oil pump blows it out when the new motor fires up. Hope all this makes sense...lol.