West towards Seattle
A page on digihitch recommends the 276 Exit near the airport. I waited here five hours with only an offer to the next town over. The nearby truckstop is unfriendly to hitchhikers, and even has a "No Hitchhiking" sign in the window (the first I can ever recall seeing in a business). There is another exit with truck stops a little further down the road (Exit 272) which may be better.
I did not try downtown, but be advised that there is little room to pull over on downtown onramps, and locals warned me that police harassment is common.
Places to avoid
Avoid the whole city, unless you have a very good reason to be there.
Accommodation and Sleep
Camp away from the downtown, as there is a meth problem here and aggressive police as well.
I have never seen so many railcops in one city.