I am moving this to behavior for you.
Ok, I just got your email and I would suggest that you take a look at this thread and see if anything clicks for you there:http://www.thecatsite.com/forums/sho...&threadid=9563
Also the medication will make your cat drool- it is part of a stress reaction as well as the taste of the medication. If the cat is peeing all over the house, you have to break down the urine with a good enzyme cleaner.If you don't the cat will return time and time again to pee in and around the same spots.
One of the best products out there is Nok-Out and you can order it online here:Nok-Out
I would also try trashing your litter pans and replacing them with new. You said the cat has been to the vet, have they drawn urine directly from his bladder via a needle? That is the easiest and the best way to find out if the cat is suffering from a UTI. If they haven't done that, I would recommend that you do this soon.
You also said he was 10 years old. I would take him in and have his blood levels checked, as this is the age to start that. Older cats can have breakdowns of internal organs and he could have something working inside of him that is causing this loss of urine. The medication he is on can also stop his urinary output, so you have to be careful and make sure that he is peeing. Also invest in a blacklight flashlight and check your home for urine stains, you will be surprised how far it can travel.