Hi, I am Dr. Peter and would like to help.
1- Is he on medication?
2- How long has he had diarrhea?
3- Any vomiting?
4- Besides the diarrhea, any other symptoms?
1- Is he drinking more than usual?
2- Did he get into anything or eat something out of the ordinary?
I think he has for the last couple of days. I don't believe he has eaten anything unusual although I noticed he had been in the cat's liter box when I came back from the store this morning. He already had diarrhea when I went out.
The more conservative approach to diarrhea yet very effective is to feed rice (75%) and boneless chicken (25%). The rice will make the stool harder. In addition, give 1 tablespoon of plain yogurt twice a day at least for 2 weeks. The bacterias found in yogurt help with regularity. Do not give immodium or pepto bismol. If within 24 hours of feeding as above the diarrhea does not improve, have him checked by your veterinarian he may need medications.
Regarding the drinking, when dogs drink more than usual it could be a sign of an infection, kidney or liver disease, diabetes and even cancer. I would recommend to consider having him checked by your veterinarian and have a blood test and urinalysis to make certain everything is ok.
If you have additional questions I will be glad to answer them.