Welcome! My name isXXXXX am a 2003 graduate from UC Davis, and currently a Medical Director of a veterinary hospital.
I am sorry to hear about this concern.
The excessive water intake is very concerning for problems like diabetes, liver disease, urinary tract infection, kidney disease.
Drinking that much water at once will over distend the stomach and induce vomiting. So, not surprised that Max is vomiting afterwords.
The hacking sound could suggest a upper respiratory infection, pneumonia (which could have been caused by aspirated some of that water into the lungs), heart disease, and unfortunately, cancer has to be on the list.
To help settle the stomach you can use of the following, but not as a replacement for veterinary examination include
1.Pepcid A.C. (famotidine) comes in 10mg, 20mg, or 40mg tablets.
You can give it every 12 hours. You can give 0.5mg per pound of body weight. So, a 20 pound dog would get 10mg.
2.Prilosec (omeprazole). It comes in 10mg or 20mg tablets.
You can give in every 24 hours. You give 0.5mg per pound of body weight. So, a 20 pound dog would get 10mg
3.Zantac (Ranitidne). It comes in 75mg, 150mg, or 300mg sizes.
You can give it every 8 to 12 hours. You give 0.25 to 1mg per pound of body weight. So, a 20 pound dog would get roughly 1/3 tablet of the 75mg. Even with bigger pets, it is easiest to get the smallest size tablet. Even a 75 pound dog would only need one 75mg tablet.
But, absolutely, some basic testing is a must to start figuring out what may be making him sick.
A canine basic blood test and a urine test (urinalysis) may answer a lot of concerns, or at least rule-out many possible explanations.
What can tests tell you:Chemistry Panel CBC (complete blood count)Urinalysis
Sorry to hear Max is not feeling well.
I hope that information has been helpful.
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