Washington's current map strikes me as needlessly messy. There are multiple incidents of two districts sharing the same county, not one district is fully contained within King County, and I don't think WA-01 is even contiguous by road. I don't know a lot of background info about dynamics of the last redistricting cycle there, but I would expect better from a commission.
Anyway, here's what I came up with:
1: Clinton +7
2: Clinton +36
3: Trump +8
4: Trump +23 (39% Hispanic)
5: Trump +13
6: Clinton +12
7: Clinton +77
8: Clinton +5
9: Clinton +40 (48% white)
10: Clinton +13
Not much change from a partisan standpoint, but a lot cleaner. Northern WA gets its own seat, as does Pierce County. All of Seattle is in the 7th, and the 9th is all-King County suburbs while still being minority-majority. As was mentioned, there's no good way to cross the Cascades, so I figured sticking with I-90 made the most sense. For all the oddities of the current map, I think the 8th district is about as sensible as it can be.
(I double-crossed 4 and 5 here because of the wacky precincts in Walla Walla, which is of course not necessary.)
Did you take into account incumbent residences? It looks like Larsen lives in your 1st (whereas according to Wikipedia, he doesn't live in his current seat) but I'm unsure if your 2nd reaches down far enough to take in DelBene's home.
I think you've also shifted Kilmer out of the 6th and obviously we don't know about the 10th yet, but that all seems like it would be fairly easy to fix.
I didn't consider incumbent homes, as I don't believe that truly fair maps should. I know California's commission is prohibited from considering them, but I'm not sure if Washington has the same rule or if they in fact actively consider them.
DelBene's tiny hometown is on the border of my 2nd but just outside of it in the 9th, so that could be changed with few implications. Kilmer is in my 10th, but could be put in the 6th while keeping all of the 10th in Pierce (perhaps by shifting the lines in Thurston).
