I think you can leave it by the curb if you own or rent the home–SPU will charge you for a large or bulky item. It isn’t cheap. If you can store it until like-mind friends make a dump run throw it in with them. The Cylinder needs to go to the hazwaste side of things–right now it is near the former South Transfer station last I checked.
Thanks to recommendations from the blog, we used GreenGuysSeattle@gmail.com (Green Guys Recycling) to pick up an old gas grill we had here. They were super easy to coordinate with and took away the grill free of charge!