YOU SAID:
you can't make him drink.
INTO JAPANESE
彼を飲ませることはできません。
BACK INTO ENGLISH
I can not let him drink.
INTO JAPANESE
私は彼に飲み込ませることはできません。
BACK INTO ENGLISH
I can not let him swallow.
INTO JAPANESE
私は彼が飲み込ませることはできません。
BACK INTO ENGLISH
I can not let him swallow.
That didn't even make that much sense in English.