Homemade hand parts tumbler possibility?

If it "tumbles" slowly, you might have something there. Folks who reload ammunition use a tumbler to clean their spent brass casings. If your device "spins", like is required to sling the water off the lettuce, it wouldn't work because the parts would not tumble around in the sand or other medium, they would be thrown to the outside of the container due to centrifugal force, and there they would stay during the entire "spin cycle". You might be better off hunting for a cheap rock tumbler for your parts cleaning - they turn slowly.