Rowing machine/ washing machine.
The fancy exercise machine in the photo isn't a washing machine. It does use
water as an
energy damper. I could see a simple version of this, being made from one of the many free pieces of exercise equipment that are advertised everyday. Or, build one.
The on-again, off-again nature of rowing strokes,
should do a good job of jostling the clothing around.
I imagine a lightweight wheel, mounted horizontally like a potter's wheel. The tub of water, with a sealable lid, is mounted on top of the wheel. If there where a pipe protruding from the bottom, a rope could be attached and wound around this axle. When the rope is pulled, the unit spins. Allow it to continue spinning until the rope winds up in the opposite direction. Pretty much like a yo-yo. That's it. I haven't built one and I don't know if I ever will, but the concept is pretty simple.