My dog has not ate in 5 days .He will drink water and has runny poop 3 or 4 times a day. I asked my vet but he said he didn't understand that either!!

Has your vet figured out why he hasn't eaten in 5 days?

If he hasn't eaten in 5 days you need to do more than ask your vet, you need to make an appointment. I'm shocked that your vet hasn't told you to bring your dog in. A dog that's not eating, and has runny poo, is in great danger, and needs treatment.

This is really odd...you're more concerned with how the dog can poop than why it's not eating....that makes little sense to me.

Have the vet figure out why the dog isn't eating...then if you get that solved, you no longer need to worry about why he's pooping without eating.

Yes I agree and it is still an issue if he is not eating. The simple explanation is many many feet of intestine that still contains undigested food and a slow metabolism.

Get him to a vet !