I know what you are talking about. Filou gets his fluids at the vet's only- for 4,5 years now every week. He is a very energetic wiggle worm but at the vet's he is a little bit intimidated which helps.
But even there once in a while he insists on pulling the syringe out.
He is good these days- active and naughty. So it's all worth while.
Good luck for Blacky- that he may be a fighter and survivor like Filou.