Welcome...I Agree with Margot......You need to find out what is causing the diarrhea, especially in a puppy...Masking the problem can lead to a huge mistake.....Get your guy/girl to their Vet tomorrow to have it checked out......Some puppy diseases can turn bad very quickly.....Good luck & let us know what you find out....Karla
You can give Pepto Bismol do digs but I am not qualified to recommend that or the dose. You might be dealing with some health issue here.
How long has the pup had diarrhea? Any other symptoms? Could be anything from Parvo to stomach upset, to poisoning, a blockage, etc.
Withhold food fir 24 hours, make sure the pup is getting fluids and give your Vet a call.