Alright, I'll be honest. I've never stepped foot in the store, and don't know a socket wrench from a hambone, but I heard that Ferguson's is a great place to get plumbing supplies. In fact it's the best in all of Seattle. My hubby-too-be frequents this store, located in the Interbay District, during his jaunts into the plumbing world.
The staff is really nice and, and the boss barbeques when it's warm out. What more could you ask for?
On a rather important side note, it's a contractor store, so common folk need not apply.