To ensure even cooking, remove the meat bag from the fridge at least one hour prior to firing up the grill, so that the meat doesn't hit the grill while it's still cold.
Gently remove the meat from the bag, and discard the bag and leftover marinade. There's not need to pat the meat dry before grilling, just make sure it's not dripping prior to placing it on the grill to avoid flare-up and burning.
Pre-heat the grill to 350F.
Sear the meat on both sides over direct heat, for approximately 5 minutes per side.
Move the meat to a medium section of your grill (in between burners is great!) and cook over indirect heat, turning as needed, until an instant read thermometer reads 130F when inserted in the thickest part for medium rare, or until you reach your preferred "done-ness".
Remove the tri tip from the grill, and let it rest in a cutting board approximately 10 minutes before cutting.
Slice against the grain and serve.