I like the design and idea, for the fins, perhaps something would work with fins of different heights or simply taking the agitator out of a washing machine.

I've watched an agitator go back and forth enough to note that it does not rotate except to go back and forth through 45 or so degrees. However, the fins work laundry up and down through the water.

If you had took the main spindle made and istead of the cross at the bottom used a few "t" sectons. I'd want four pvc fittings like: http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=13670&product%5Fid=18403

At the bottom, the joint would tie into the bottom of the barrell. The two pipes that extended from that would be tied to fins that were not on the next fitting up but on the one that was second from the top. The two other fittings would also be attached.

All this seems like a lot of work. Wouldn't it be just as effective to have a barrell, fill it with water and detergent, add a couple clean smooth rocks or something else solid to agitate, and then roll it all around. When done, rinse either using the barrell or not. Use a detergent designed for sensitive skin, youor rinse is likely to be not that effective, so something that does not irritate is better as a detergent.

Finally, be careful with and where you dispose of the wash water and rinse stuff. You need to pick what places you intend to use to consider as contaminated.