Turn crock pot on to high. Combine all spices and seasonings in a small bowl.
Finely dice the onion and spread it out on the bottom of the crock pot.
Spread half the seasoning mix on one side of the beef. Place roast beef in the crock pot, seasoned side down. Spread the rest of the seasonings on the beef. Pour 8 ounces of beef around, not on, the beef roast. Cover, let cook for two hours; turn over and continue to cook for two hours.
Remove the juices from the crock pot with basting syringe, leaving the onions in the pot. Add 1 cup of bbq sauce and spread over top of roast beef. Continue to cook on high for one hour.
Using two forks, shred the beef. Don't worry if there are larger chunks of beef. They won't be there for long!
While the beef is cooking, strain the juices through a cheesecloth into another pan or bowl. Reserve for the beef. Add along with the bbq sauce to maintain moisture.
Add second cup of bbq sauce and 1/2 cup of reserved juices. Change crock pot setting to low. Continue to cook on low for one hour.
Add the last cup of bbq sauce with 1/2 cup of reserved juices. Shred the beef further. Let cook for one more hour.
To reserve and eat as needed, place crock pot on warm setting and stir to maitain moisture. Add reserved juices as needed. Serve on hoagie rolls, Kaiser rolls or Texas Toast.