Hello,
Wowza. That’s quite a story. I think I would recommend the following options to discuss.
1. Seek a feline exclusive practitioner. If available they are really helpful for the tough cases.
2. Consider an ultrasound.
3. Add cosequin daily
4. Consider an iv fluid hospitalization to really flush out the bladder
5. Xray of the body. May or may not need to do if doing ultrasound
6. Add a fountain, feliway and lots of litter options. Even a very low litter box like a baking sheet.
7. Environmental enrichment. Toys. Catnip. Window seat with bird feeder view. Etc.
Let me know what happens.
An update: he’s calling two local rescues for help. I’m leaving this up, however, so folks can share input should someone come for the same situation.