WindSparrow, my vet gives me plastic fake litter. So cat pees in box with a little plastic litter, and then I pour through a coffee filter into the collection cup. I left her in there while I was gone and I think I have enough for them to test.
My vet clinic doesn't love the plastic litter. Their stance on it is that it does not help. I have to get it from the vet clinic in the next town. They sell it in a kit with a nifty stout plastic litter box liner that doubles as a collection receptacle. What works for Harvey is for me to clean and sanitize the litter box, add fresh new litter, put the liner over the regular stuff, then add about half the plastic beady things (incidentally, if a craft store near you sells cheap plastic seed beads, it's the same stuff). Then I lock Harvey in the bathroom, with all the rugs and towels removed in case he gets tempted. Typically speaking by the time I make my middle of the night trip to the toilet, he's done the deed. So I tie up the plastic liner, put it back in the package it came in that has a ziplock, and then put that inside several layers of plastic grocery bags, and the whole kit & kaboodle into the fridge to wait for the office to open.
Harvey is sitting here sending his best purr vibes to all the Buffista kitties having to deal with urinary tract issues.