[Wally Arntzen]

The best way to manage the one tank system is as follows. 1. When parked in an RV park and hooked up you should keep the valve closest to the end open and the one from the tank closed. This allows the water from the kitchen sink, bath sink and shower to go directly out of the coach and down the drain. You keep the valve next to the holding tank closed and when it gets 3/4 or more full you dump it and close it again. My wife and I are full timers and it takes about a week or more to get the tank 3/4 full which from the toilet use only.
2. When traveling on the road you keep the outside valve closed and the tank valve open, this allows all of the used water to merge into the tank and when you get the tank 3/4 or more full you have find a dump station or an isolated country road where you can pull your cheater dump and let er go. Richard is right if you are traveling and do not open the tank valve you will have back up in the shower or overflow on the top of the tank in the bay.
I think the one tank system is superior to the dual tank system any day.

Thats the fat mans 2 cents worth and i'm sticking with it.