I just checked the website and there is a 626 but not a 625. That said, there are 6 models listed and only 2 (which does not include the 626) that have a gray water tank listed. I have never owned a TC but my popup had running water but no grey tank. The sink drained directly to the outside where I had a short piece of hose draining to a 6 gallon jug. The discharge point in the wall of the popup had a cap on it. If you are set up the same way, but you didn't open the exterior cap, the sink water has no place to go.