On my latest trip to Clatsop County, I decided to sample several offerings of clam chowder, which I usually avoid. The experiment was a big disappointment. Northwest-style chowder should not be thickened, yet nearly every restaurant seems to strive for a consistency somewhere between Elmer's glue and library paste. A claim that chowder is "made from scratch" is no indication of quality — that one was one of the worst.
I'll note only two exceptions. The Ship Inn in Astoria has a chowder which, while not exactly thin, is rich and creamy rather than obviously thickened. Very nice.
The second is the Bell Buoy Restaurant in Seaside. This is just a small, temporary-looking building next to the venerable Bell Buoy seafood market. I had never gone in there before despite my frequent trips to the town because it didn't look like much of a place to eat. Nevertheless, they have a fine clam chowder which is properly thin and which contains a mix of razor clams (for texture and flavor) and sea clams (for more flavor). Most chowders in the area do not contain the local razor clams, which are more expensive. You can get the BB chowder to go, in quarts if you like, and take it somewher nicer to consume.
Tip: I like cayenne in my chowder (and oyster stew) in preference to Tobasco Sauce, because I don't want to add vinegar. Most restaurants will have cayenne in the kitchen and will send some out, but it's likely to come from a large institutional jar which has been on the shelf for a few years. Almost no restaurant will have a shaker of fresh cayenne, so I now travel with my own supply in a waterproof shaker.