Thanks for the info. Are you saying that those vacuum pumps from harbor freight wouldn't cut it?
I don't have any experience with them so I can only guess. But the pump has to be high quality to pull the vacuum needed, it must not leak back through the pump during the "leak test" period, and the gauges must be accurate enough to tell you what the vacuum level is and whether it changes over the time period of the leak test.
My experience with Harbor Freight is that the tools fall into one of the following three categories:
1) Work pretty well and last a reasonably long time ... (rare, IME),
2) Work OK for a while and then fall apart,
3) Total junk right out of the box.
Since category 2) is the most common, I look at Harbor Freight as "rental" -- if what they cost is what it would be worth to you to use them twice and throw them away, then they're "worth it". But generally, the more high-tech an item is, the more likely it is to be category 3). I'm not saying not to try the Harbor Freight pump and gauges, but don't be surprised if they don't work for you (** in my opinion **, other people have had different results).