Originally Posted by FreshAir
I just look down the toilet pipe into the tank.....if the s**t is nearing the 'pipe' it's full enough.
Heh... that's the method I actually USE, but that's not the question asked.
If I put in a gauge it would be on the gray, but if I were getting in far enough to slap a sensor on that tiny little gray tank, I'd be putting in a bigger gray tank!!