Paul,

To do a gross leak check with the least trouble, simply pull a vacuum for five minutes or so, then close off both low and high side of your manifold and see if it will hold the same vacuum for a minute or two. If it does, then go ahead and do a thorough evacuation. If it's going to have a sizable leak, you don't have to completely evacuate to tell, and that way you won't waste your time on a full evacuation only to find that something needs attention.

Good luck,