I am not totally certain but am pretty sure there is no tank. This is a new trailer for us and was told by the dealer at the pdi that the valve by the drain would drain the tank. Makes sense right? I go to put water in the sink and it fills up automatically with water. Only way to drain the sink it is to open the drain valve at the rear of the trailer and the water in the outdoor kitchen sink goes down. I call the dealer and tallk to someone else he says that there is no tank for the outdoor kitchen. So maybe this is normal?? That's why I asked the question in the original post. Can't see anything under the trailer because of the enclosed underbelly.