Take a tub - like an old unused litter box - and fill it with warm water. Fill a large bucket with warm water too. Put the litter box in the bathtub and the bucket just outside it. Make sure you have something to dip water with.
Then get into the tub with the cat, holding him/her firmly under the chest, and lower him/her into the litter box full of water.
Sit or squat in the tub behind the cat, allowing him to grip the edge of the litter box but maintain your hold on him. Use your free hand to scoop water up over him and wet him before putting the shampoo on and soaping him up.
Once he is as clean as you want him to be, start using your scooper to rinse him with the clean water from the bucket.
When he is rinsed, empty out the litter box and wrap the cat firmly in the handy towel I forgot to mention above. Hold and gently rub him until he is halfway dried off and begins to squirm (my cat acts like he's in shock for a while once I've got him wrapped - or maybe he just likes being held and comforted).
And there you have it - clean cat and no shreds!