I've been using wood chips for three years now, more expensive but easier to wash out and smells good. Again, gets expensive with a kennel full like I have. I am wanting to get all my houses changed over to barrels this summer (already have the barrels sitting & waiting) they hold the wood chips better (not as easy for the dogs to dig it out) and takes a lot less to fill them up too than the big dogloo houses. Just gotta get out there and get em built.
To answer your question, I cleaned them out 2 months ago Bill.