Hi!
Welcome! You'll love this place
I'm sure you'll get a lot of good info on here.
My first concern is that he's drinking so much water. I'm sure you've talked to your vet about this, but I think that perhaps it would be a good idea to have some blood tests done. Excessive water drinking can be an indications of diabetes and the frequent peeing, although probably caused by all the water intake, could be an indication of a UTI. It's very possible that he simply can not help this behavior. Also, as pointed out by Sunnie, if he's not neutered, that could also play into this. Blood tests are a quick and relatively inexpensive way to rule out a lot of questions.
Assuming it's not something medical, going back to the potty training methods may help, but you may also want to invest in some belly bands. This won't stop him from marking/peeing, but it will help with the unpleasantness of cleaning up accidents. There are several YT members who make them, or you can do an internet search for belly bands to find them.
Good luck, let us know how it goes. OH!! And post pictures of all your babies as soon as you can.
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