Thoroughly clean the toilet. Put both lids of the toilet up and add 1/8 cup of pet shampoo to the water in the bowl. Catch the cat and soothe him while you carry him towards the bathroom.
In one swift, smooth movement, put the cat in the toilet and close both lids (you may need to stand on the lid so that he cannot escape). CAUTION! Do not get any part of your body too close to the edge, as his paws will be reaching out for anything they can get hold of.
Women come from Venus, men come from Mars, but where the hell did this come from...?
The cat will self agitate and make ample suds. Never mind the noises that come from the toilet, the cat is actually enjoying this.
Yeah, sure... looking totally underwhelmed...
Flush the toilet three or four times. This provides a "power wash and rinse" which I have found to be quite effective.
Throughly appreciating the effort being taken.
Have someone open the door to the outside and ensure that there are no people between the toilet and the outside door.
Stand behind the toilet as far as you can, and quickly lift both lids.
The now-clean cat will rocket out of the toilet, through the bathroom and run outside where he will dry himself. Both the commode and the cat will be sparkling clean.
However, after said procedure, the cat will go and go hide itself under the house, getting itself totally dirty again.
Repeat above procedure...