Depending on the size of your water tank, checking its level it will give you a ball park figure about how much water you've transferred from the water tank to the gray water. I can't remember the gray water tank capacity, but let's say it's 25 gallons. If you have the 25 gallon water tank (which never in my experience has held 25 gallons) and you have not used the toilet but have showered, washed dishes, etc, all that water has been dumped into the gray water tank. If you then refill the water tank and NOT emptied the gray water tank, the only place that extra water can go is...back up into your sink. Or shower. Not nice. Nor sanitary or hygienic.
Now when you're connected to city water, you don't have any idea how much water you've dumped into the gray water tank because it bypasses the water tank and goes right to gray after use. So you might find yourself again, standing barefoot in nasty gray water (it could be worse, it could be black) because you forgot to empty the gray water tank.
If you go to Little House Customs' website, you can purchase a sticky backed label to install on your water tank that will give you a good idea of how much water you've used. IT won't tell you how much is in the two tanks but it will tell you how much you can figure out is in either or both.
If you plan on dry camping or boondocking for any length of time, you might want to get a bucket to periodically drain the gray water tank. NOT the black, no sir, do NOT drain it on the ground.
Whenever we pull from a campsite, the first thing we do is find a dumpstation, where we dump the black and gray.
Plus we do not shower in the camper, but use the campground facilities if at all possible, and take cat baths when we can't. Also, we do all dishes clean up outside. Most campgrounds have a dishwater disposal tank where you can dump dishwater. This saves us a lot in gray water tank capacity.
Oh, and the battery monitor is a battery saver. DEFINITELY get one. It plugs into the socket over the bed.
I hope this 'splains things.
Edited by Meadowlark, 08 October 2016 - 12:53 PM.