The problem I've always had with the "tumbler" composters is that they tend to freeze solid in winter and generally aren't big enough to get "hot" enough to work with any real speed.
When you read about composting, you tend to hear you need a minimum of a yard of material to really make it "work". Most tumblers don't hold that.
That being said, even if they don't work "fast", stuff still rots.
@eaking - you may want to just sift out the unrotted materials from your "almost done" composter and add the un-decomposed chunks to your "almost full" composter, and use the rest and start filling up that empty composter.
When you read about composting, you tend to hear you need a minimum of a yard of material to really make it "work". Most tumblers don't hold that.
That being said, even if they don't work "fast", stuff still rots.
@eaking - you may want to just sift out the unrotted materials from your "almost done" composter and add the un-decomposed chunks to your "almost full" composter, and use the rest and start filling up that empty composter.