Hello and welcome to Just Answer. I am a licensed veterinarian and would be happy to answer your questions.
Can you tell me exactly what symptoms Hughi is exhibiting? Is he straining to pass urine? Is he passing any?
Yes he is straining and some urine has been coming out.
The only thing that you can do at home is to provide and encourage him to drink as much clean fresh water as you can. His symptoms are very concierning and should be evaluated by a veterinarian right away. Any male cat that is striaining in the litterbox needs to be evaluated right away. Even if some urine is coming out he may be partially obstructed an on the way to become fully obstructed to the point that his urethra becomes plugged. This can be a life threatneing situation.
Even if his urethra is not obstructed at all, the straining may be a sign of inflammation of the bladder and that needs to be treated. Possible causes include bacterial infection, bladder stones or inflammation due to unknown cause.
Let me send you a link with more information.
I would recommend having him examined today by your veterinarian. This should be considered an emergency situation.
Do you have any further questions?
Thanks for your help.