Thankfully, our cat would not dream of getting dirty and thinks that a walk around the patio is more than enough exercise. However, I had a thought after reading this thread. One of my kids has an old stock tank near her back door. She has it full of gravel and soil so she can grow herbs in it. But it seems to me that a tank would be appropriate either for a paw wash or a full dog version. They can be plumbed pretty easily. I have a catalog from a farm supply house that may have the info if you would like a quick idea of sizes and prices for new ones also.