Transfer the steak to your
slow cooker and add ¼ cup of water to your skillet to deglaze the pan. Scrape up all the browned bits in the skillet (the water will turn brown) and pour it into the slow cooker over the steak. Add the marinara sauce and crushed tomatoes and stir together. Spoon the sauce over the top of the steak and place the lid on the slow cooker. Cook on low for 5 ½ - 6 hours.