The most common semi-automatic washing machine model is the twin tub model. One tub is dedicated for the washing of clothes, while the other is for spinning the clothes and drying it out. In these models, the amount of water to be filled in the machine is manually controlled by the user by adjusting the flow of water at the faucet.
The outer shell of the machine is usually made out of plastic. This ensures that the machine never rusts. Newer models come with transparent top lids that ensure that you can keep an eye on the clothes as they wash or spin without actually stopping the machine and opening the lid.