Hi try picking him up a waterpik - running it on the lowest setting with Luke warm water and maybe a bit of alcohol free mouthwash will clear out the guck and make him feel fresh for a bit. I still love mine.
Alo try getting club soda - flatten it - let it sit at Room temperature if he's sensitive to temp. Then he can swish and swallow it will help his throat and hydrate him. Plus it too helps with he guck. This is an later native to the baking soda mixture which you can swallow. It was recommended by my hospital. Best of luck.