I usually buy thick sliced boneless pork loin, I have also used regular pork chops bone-in, it would probably even work with a pork roast...not sure, I haven't tried that.
-Pour 1 to 1 1/2 bottles of your favorite BBQ sauce over the top. I use hickory flavor. Then, sometimes if I remember I throw a whole peeled onion in. Doesn't really matter.
-Discard the liquid (and the onion if you used one) and return meat to crockpot, then add another bottle (or more) of Hickory BBQ sauce to the meat and stir it all in. You may wish to put the crockpot on low to keep the meat warm.
-Serve on hamburger buns.