I hope Fritz is feeling better soon.
My dogs usually will not eat accept for grass
when they have tummy
upset. The grass helps them throw up.
(Rocky will usually have a loose slimy stool when his
tummy is bothering him.)

They also fast once in awhile which is normal for them.
When they do fast, they still act their normal self and their
stool looks good. They just do not eat and only drink.

I am glad Fritz is drinking. If Fritz is acting not his normal
happy self, such as lethargic etc. stool
loose, and he has been like this for 48 hours,
I would take him to the vet tomorrow just to be on the safe side.