Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about the amount Hughie urinates in comparison to the amount her drinks.
If he is getting a lot of table food or eating canned food he may be taking in a lot more fluids than you realize. Canned food can be 80% moisture, which is a lot of fluids.
Of course the fact that he is urinating quite a bit is concerning because that could indicate that he has poorly functioning kidneys or some sort of metabolic disease (like diabetes or liver disease) that is causing him to need to flush out more wastes than usual out through his urinary tract.
Ideally I would measure the amount of water he drinks over a 24 hour period for a few days to see how much he is taking in. It may be more than you realize, and because he is small it may not seem like much until measured. Put out a certain measured amount of water and then measure what is left in 24 hours. Do this several days in a row.
And I would have him examined by his veterinarian and have a urinalysis checked for concentrating ability, the amount of protein, bilirubin, and glucose present and any signs of crystals or an infection as well as some basic bloodwork, a complete blood count, biochemistry and thyroid profile.
Please let me know if you have any further questions.