Mix together the spice rub in a large Ziploc bag, shaking it to combine the spices thoroughly. Add the pork shoulder and vigorously shake the bag until the pork is fully covered in the spice rub. Place the bag with the pork shoulder in the refrigerator for at least 8 hours (the longer the pork is allowed to marinate, the stronger the flavor will be).

On cooking day, remove the pork shoulder from the Ziploc bag and place it in the crock pot. Add the ¼ cup of water, if desired, and place the pot on low. Cover the pot with the lid and allow to cook for an hour. Turn the pork shoulder over after an hour and continue to cook for another hour. Turn the pork shoulder over one more time and let it continue to cook for another four hours. After six hours, check to see if the pork is starting to tenderize. (Note: You do not have to turn or check the status until 8 hours- trust me, I have made it enough times and it is fine without those extra steps). With the larger pork shoulder, the estimated time for tender meat is about 9 hours total. If it is, shred the pork using a fork (or tongs) and stir the shredded meat around in the sauce created during the slow roasting. Cook for another 30 minutes to an hour (depending on your crock pot). You can serve the pulled pork by itself or with a barbecue sauce (but honestly, it's not necessary).