The Troxel decision effectively ended third party visitation in Washington. So, there is no law allowing grandparent visitation. There is a category called "de facto parent" which can, under certain circumstances, find that a child is so closely bonded to a person that the person should have regular time with the child. You'll want to consult with a family law attorney to see if there are any facts in your circumstances that can support this.
As stated, grandparents visitation rights are in a state of flux in Washington. If you truly believe that the child should be in your custody and the child's current environment is deterimental to the child, you can file a third party custody action which would allow you to ask for visitation rights while in the midst of the litigation. The problem is that you would have to allege that the custodial parent is unfit which of course is a nasty proposition, especially when the custodial parent is your own child. Think long and hard before taking such action because filing a third party custody action could emotionally rip the family asunder.
The best way to approach the problem might be to get the cutodial parent to agree to a third party custody order.
As mentioned, in Troxel v. Granville, the US Supreme Court found parts of the third party visitation statute unconstitutional. However, at least one post-Troxel decision by a WA court has recognized that a de facto parent is consitutionally the same as a bio parent of adoptive parent, and therefore would have visitation / custody rights.
to be recognized as a de facto parent, you must show:
1. the bio/adoptive parent consented to the de facto parents' parent-like relationship w/the child
2. de facto parent and child live in the same household
3. the de facto parent entered into the parental relationship without expectation of financial gain
4.existence of bonded parental relationship.
I have a case where I am trying to prove existence of de facto parent right now.