Definitely clip the nails, or make sure the vet does that for you.

Even if Cassy does not wear a collar, getting one and having him wear it while bathing will aid your ability to hold him when he's wet and slippery.

Hopefully your sink or tub has a sprayer, use it, BUT cats hate the sound/sensation of the spraying motion, so keep it close to the skin to prevent that feeling of the water "raining down" on them.

When I need to keep shampoo on a cat for any length of time I close them in their carrier. Easy to rinse out when you are done and you know exactly where they are, not hiding (soaking wet) under the bed.

If all else fails, find a pet groomer that does cats and consider it money well spent.

GOOD luck!