I agree with above....just cycle it a couple times, then use it.
Look at it this way... you use it first time, the air compresses. You push it opposite way, now that side fills up with oil. You cycle back and now you have both air and oil. Air is compressible, oil is not.
Air compresses and when you discharge the oil out of that side of cylinder, (by pushing cylinder the opposite direction) the air (in small bubbles) goes out with it to the holding tank where the air escapes. Easy Peasy and you didn't have to worry about it.