My husband has seen many doctors for the same problems. Thick, glue like mucos and inability to swallow. He is also 16 years post radiation with a small portion of his tongue removed. He had a peg installed 3 years ago and has accepted the fact he will not eat again. What did help was to get a button tube. Since it is low profile, very small, and the extension set can be removed when needed for a feeding, it provides a certain amount of normalcy. I strongly recommend Applied Medical Technologies MiniOne non ballon button.

My husband has also started using a portable oral suction machine for the mucas. This may be something your father might want to try.