Code books can be purchased from Seattle Dept. of Planning and Development (20th floor Seattle Municipal Tower). There are also some other websites where you can purchase them:

• Washington Association of Building Officials
  Code books and code information
  
  
• International Association of Plumbing and Mechanical Officials
  Code books and code information
  
  
• International Code Council
  Code books and code information
  
  
• Washington State Building Code Council
  State law regarding construction related codes
  
  
• Washington State Department of Labor and Industries
  Contractor registration and plumbing installer certification