Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your fellow has been drinking a large amount of water and subsequently urinating much more and drooling excessively, lip licking, as well as having changes in stool color and consistency and increased gas. I understand that he has foul breath odor as well.
Is he losing weight?
Has his appetite increased or decreased?
Is he running a fever?
Possible causes behind his symptoms include metabolic organ failure, including kidney or liver disease, or diabetes.
Dogs with organ disease can become quite nauseous which could explain his drooling and lip licking.
When organs begin to fail they will often drink more as a way to flush out excess waste products or as a way to try to maintain hydration when fluids are being drawn out of the body via waste products being excreted out through the urine or in his loose stools.
In diabetes for example large amounts of fluids are being excreted because as excess glucose is excreted out through the kidneys water follows, so these pups actually become dehydrated.
Metabolic organ failure will change the bacteria population in the gut due to changes in waste products, that can lead to changes in breath odor and/or gas. That will also lead to changes in stool color and consistency.
An infection that is systemic (multiple places in his body) could also cause his symptoms.
I highly recommend your fellow see his veterinarian as soon as possible for an examination, bloodwork including a complete blood count and biochemistry profile, and a urinalysis. The sooner that we can figure out why he he has these symptoms and get treatment started. The earlier we start treatment the better chance we have of being successful.
Please do not restrict his water. Whatever is going on he needs to drink as much as he is.
Please let me know if you have any further questions.