1) Most scholars have ruled that washing machines do purify clothes. When najes clothes are washed and rinsed, upon the release of water from them (when the washing machine spins), they become pure. It’s like having a container with a najasa in it. You pour water in it, then rinse it, and when the water is spilled out the container becomes pure.
2) Some scholars have indicated that the water which splashes back (this happens in washing machines that have the lid on top not the side) is najes and makes it all najes again, but most scholars do not agree and they consider it pure.