Fire the pit up hot - over 300* and use bacon grease to season the interior grates (like a cast iron skillet).
Keep the pit at temp for a few hours. Some use PAM spray or canola - a high temp oil.
Lang suggest closing upper damper to "smoke cure" the grates for a couple hours.
I also coat the exterior for some weather protection... allowing the grease to bake on.
Cooking at Mason-Dixon BBQ Services
Lang 84 Deluxe Kitchen known as "The Glamazon" , Custom Klose Backyard Chef... of Snot, and a 22.5 WSM
Lang 60 Mobile - The Damsel II, Lang 48 Patio - The Damsel, Bubba Keg Grill - RIP, Double Barrel Smoker and a BSKD