A growing number of retail locations will take your old propane tank in exchange when you buy a new tank, or need to refill your old barbecue-size propane tank. Some of these opportunities are found at your corner convenience store that also sells fuel. At this time there is not a comprehensive list of where these services are offered, so you will need to check with your local stores.
Blue Rhino provides one propane tank exchange option for barbecue-size propane tanks. Their website lists locations in this area, using a zip code search.
See the yellow pages for other possible options provided by propane dealers including options for larger tanks.
If you cannot find a business that is convenient and suitable, residents can recycle barbecue-size, or smaller, tanks at all Snohomish County Solid Waste facilities.