Not your favorite part of boating... but has to be done. Below you'll find where you can pump it out yourself... or mobile services that will come to your boat and do it for you. Always TIP the operator!
Including the San Juan Islands. From Washington State Parks Boating Program.
Seattle area pump-out stations. From Washington State Parks Boating Program.
This isn't a very complete list (compare to the resource shown to the left), but it is state-wide. Locations and details on boater pumpout stations in Washington. Provided by Sport fish restoration Trust, Washington State Parks and Washington Sea Grant, using Google Maps