Anthony Del Negro's “Grayson” finds its protagonist riding high after selling a piece of his art for $60,000. With pressure from his agent, Wendy, to replicate that success, he retreats to his family’s cabin with the intention of focusing on his work. The place had been unoccupied for some time, and the condition of the plumbing—a blockage apparently extending all the way to Chicago—necessitates calling in local assi…