The little washer thing actually works well enough that I am trying to figure out how to make one out of metal. (Old pressure cooker maybe?)

It works because it is sealed. The warm wash water heats the air, pressurizing the load of laundry. This drives in the soap to get a better cleaning. In my experience it works better than a washing machine. It gets my clothes cleaner and subjects them to less wear. Great for small loads like one or two sets of cycling clothes. It also uses less water and soap.

BUT, that particular product is made of plastic that doesn't hold up too well. The bushings creak, the handle and stand flex, and there gets to be a lot of wear on the important parts of the lid.

It was a good proof of concept for me. I just wish they made one that was more durable.