Hello Benjamin, this may seem a bit off the wall, but I regularly use plaster disolving solution for removing post soldering off silver soldered appliances. This is in conjunction with an ultrasonic cleaner, but soaking your soldered items over night in the solution would work. As I am "across the pond" from you I do not know what USA propriety brands are available. If you know any Dental Technicians or Dental Laboratory suppliers, give them a ring and I am sure they will be able to put you on the plaster disolving solution I mean. I have used this method for years and the joints are perfectly clean. I hope this is of help to you
Regards
Pete