I would make sure he has plenty of fresh water available. If you're really concerned, you could offer him some boiled chicken and rice for his next meal, it's super mild and easy on the tummy. Pink Bismuth CAN be given to settle and upset tummy in dogs, but for that I'd call a vet and ask.

Poor guy, I hope he's feeling better soon. When Jasper got Giardia he decided to announce it......explosively.....at around 3am, so I know how that goes. -_-