<b>Hello, I wanted to try out the black tank flush port today for the first time (using clean water on a previously emptied tank). I carefully read all of the instructions and reviewed the bathroom vent and drain diagram. Both reference a shutoff valve that must be opened before flushing the tank. I located the incoming water line under the front dinette seat, but there was NO valve anywhere. I then hooked up a hose and slowly added water which I could see (clear inlet hose) and hear water filling the black tank. When I opened the black tank tee handle at the rear, everything appeared to flush properly. My question is.....did the factory forget to install a shutoff valve or has there been a design change? I can cut in a valve, if needed. Thanks, John</b>