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It should start to work in a few hours. You can repeat it after 4 to 6 hours if he is still loose.
There are many causes of diarrhea. Some will affect the appetite, and others do not.
You can test him for dehydration by gently pinching skin over his shoulders and releasing. The skin should go back into position in less than one second. If it takes longer, he is dehydrated.
Check his gums; if he is dehdyrated or very ill, his gums would not be pink but pale.
Try to get him to take broth or ice chips or Pedialyte as well as water.
I would let him rest.
Sorry I was away.
Vomiting with diarrhea worries me more. The first thing I think of is parvo virus, but since he is vaccinated, that is less likely.
He probably should see a veterinarian, for an injection to slow the vomiting, to see if he is dehydrated, and to be checked out. Are his gums still pink?