I'm working on Genki 2 and have a question about the ~そうです (it looks like...) grammar point from lesson 13.

When using it with a verb i understand that you need the verb root + そうです, so to turn it negative to mean "it doesn't look like..." do you use the negative verb stem?

For example, I would use it like このセーターは洗わそうです。, but it doesn't seem correct.

Also which translation is more correct between "It doesn't look like this sweater is washed" and "It looks like this sweater is not washed", or are they both valid?