The liquid is water from the meat being pulled out by the salt in your rub. Try putting the rub on for only a couple of hours.
I usually put the rub on my ribs for an hour or so. I also do a 4-1 method where after 4 hours I put the ribs in a shallow pan and paint the ribs with butter, sprinkle on a little brown sugar (and maybe a little rub) and drizzle a little honey on them then cover the pan with foil. After another hour they are usually done, if not, I baste with the drippings in the pan and give it another 30 min or so. I also use Meatheads Memphis dust rub so I can keep the amount of salt down.