Hello @phyllisg. I had radiation that involved my ear area with mouth involvement, but not throat so swallowing remained for me. Pain was helped by a "Magic Mouthwash " mixture from the hospital by prescription and that was swirled and spit out. I also used a topical oral lidocaine gel liquid for pain just prior to eating. I know many patients will need a stomach tube at this point, does your husband have one? Here is a link to another discussion about swallowing dysfunction: https://connect.mayoclinic.org/discussion/cricopharyngeal-dysfunction-difficulty-swallowing/

There are saliva substitutes available by prescription but I have never asked my doctors for that or had experience with it to thin the mucous. Keeping well hydrated will probably help but if he cannot swallow??? During the final weeks of radiation at UMichigan I was getting a liter of IV fluids twice a week as I just could not stay hydrated orally. That helped a lot. Will you be seeing your nurse practitioner or doctor soon to ask about his issues? If not, I would put in a call for help. That's what they are there for.
This is a very tough time with radiation therapy and I wanted to give up at this point, but was encouraged by the nurses to stick with it. It does get better. Help him to be strong and keep advocating for him.