Just dump plain water in and and see where it comes out. The two outlet valves are right beside each other on mine.
I have two tanks on my 92 Dolphon. I took a bucket, marked the gallons on it with a marker (used a gallon milk jug) and measured how much water it took to fill it. Both tanks hold about 12 gallons (how full is full?). I also checked the calibration on my tank gauges while I was doing this.
I found out the kitchen sink is the only input to the gray water tank. Needless to say, we use the bathroom sink and the toilet the most when we are camping. The black tank fills up in a couple of days. I would like to replace the two tanks with one. I don't see any need to have two tanks anymore, everything is dumped now adays. Years ago, you could dump the gray water anywhere in the campground, they used to tell us at the Federal campgrounds to "dump it around the trees" to kill the insects.
Any one ever try replacing the tanks to have one larger one?
