I've put together the guide (link below) to waste and resource centers around the greater Seattle area. This includes recycling facilities, wastewater treatment sites, composting centers, landfills, and our local watershed! If I've missed any that should be added to the list, please leave a comment below.
Most of these centers offer tours, but for private tours they request groups of 10 or more. If you're interested in touring a facility as a group, please email at firstname.lastname@example.org