My father has a severe saliva problem

Hi, my father is 50 years old, and for the majority of his life he has had excessive saliva. He is constantly spitting out saliva. Large quantities of it. He sleeps with a spit bucket next to his bed. He says that he feels the area surrounding his tonsils fill up with spit, and the amount is so excessive that he needs to expel it. He eats poorly, and has bad digestion. He says that his mouth feels acidic. What is wrong with him? Does he have low stomach acids? Is there anything he can take to help him with this condition? Thanks.
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