There are several devices available; "Harbor Freight" has a A/C vacuum that operates off of an air compressor for a very small price, under $20 as I recall.
To truely do it right you can get a A/C vac from on-line sources like
www.acsource.com, they will run in the $100's but they do an excellent job. Many of these also come up on Ebay from time to time, for around $60. I have a "Robinair" A/C vac that I have used for years with great success. It's electric and I just attach it and let it run for a few hours to insure that all of the excess moisture is gone.