It is legal here in Washington State. I live here too. I have done tails and dew claws at home on my own puppies and also helped my friend with her GSD pups.
How do you do it? I have seen it done several ways. It is BEST to removed dews after the pups are two days but no older than three days. This is because you don't want to wait for the toes to be growing fast and gaining nerves and lots of connective tissues -- and -- if they are fully articulated (meaning there is bone holding them on) then you definately want to do them early so the bone dosen't harden.
Removing a body part from an animal is brutal. Young or not, it is not a thing that will make you feel really good.
I have done it on small breed puppies with human toenail clippers. It is fast and accurate, not to mention the clippers are very sharp and easy to sterilize. There is a better way though if you have larger breed puppies (such as a Lab or Shepherd)
Get a hemostat surgeon tool (you can order them just about anywhere online that sells medical supplies). Clip the hemostat to completely dislocate the dew claw. The pup will squeal ( ). Then have a scalpel or a razor ready to cut. You can use the hemostat as a guide to make a very clean cut, the puppy won't feel the cut at all due to the hemostat clamp. Have some styptic powder ready, before removing the hemostat you apply the powder to the wound. Go as fast and accurately as you can and the pups should have minimal pain. Usually they go back to nursing without hesitation.
IF your puppies are older than three days..I wouldn't do it yourself, take them to a Vet and have it done.