Slow Pokes Brisket Shack in Manchaca, south of Austin, one of the most unique BBQ joints the Posse has ever visited. (Photo ©Chris Wilkins/Texas BBQ Posse) We arrived at Slow Pokes Brisket Shack in Manchaca, Tx., a little after noon on a recent Friday. No more than 60 seconds later, Posse co-founder Chris Wilkins declared: “This is the most unique barbecue joint we’ve ever been to, man.” Wilkins has never been more right. Visually, Slow Pokes Brisket Shack, located in a rural area not too far south of Austin, is overwhelming. It’s a hoarder’s paradise that had its beginning about…