What form would I be filing in the state of Washington to motion default on a parenting plan and motion for full custody

The forms are at http://www.courts.wa.gov/forms/?fa=forms.static&staticid=14.  The precise form or forms that you need depend on your circumstances.  I am presuming that you are asking about obtaining default on a petition and proposed parenting plan.  If that is correct, then you need to file a  Return of Service (or an acceptance of service) showing proper service of the petition, summons and proposed parenting plan.  You will also need to file a motion for entry of default plus you will need to note the motion for a hearing.  You will need to serve the papers you file on the other party.