When I tighten a belt on a WP/KM, I use a pry bar on the motor bracket to put tension on the belt. Keep the pressure on the bar until both bolts in the motor mounting bracket are tight. If the belt is brand new, I tend to tighten it a bit more, because a new belt will stretch a bit after it has been ran for awhile.
New four port pumps are only about $25.00 to $30.00, so if your pump is not simply clogged, it may be best just to replace your pump rather than try to rebuild it.