Gotta have a shop do it Dan. They need to suck it out and then put it in a vacuum for about 30 min to boil any water out. It would be a good idea to change the reciever/dryer after they suck it out, but before the put it in a vacuum. The rec/dryer is a filter, and on the cars I work on, it gets changed out every 2 years and gets all new refrigerant with it.
Steve
P.S. if they try to charge you a ton of $, tell them the R-12 is $40 per pound, and you have over 1 lb in the system, that you will give to them. They can recycle that and sell it.