You can sprinkle barkeepers friend on the rust stains, it will take out some. I would sprinkle it on and make a paste by splashing it with water let it soak without drying, rinse as much as you can off with a hose or under facet then wash like normal. You don't want to scrub it in, you just want the Oxalic acid to work, if you have Oxalic acid for teak that would likely work as well but I always keep Barkeepers Friend around, so I have used it.
I have one of the Wonder Wash machines and it works OK, but is great for sweaters, and other knitted items. Not much more than a 5 gallon bucket with a tight lid, doubt I will take it on the boat as it is big and really serves only one purpose. It is also very flimsy, I think they used to use metal axles but are now plastic and the stand keeps falling apart on mine. The spin dry is really good, a pair of heavy jeans will dry in an afternoon after a cycle of two (normally will get funky before they line dry where I live).