How long should I cook a 2.5 lb pork shoulder?

I bought an already seasoned with bbq rub, 2.5 lb pork shoulder tonight and want to cook it in the crock pot tomorrow. I figure low for 8 hrs is good, but should I put some kind of liquid in it? If so, what would you recommend? I am going to have pulled pork sandwiches and coleslaw, and maybe some corn! Thanks for the help!