Originally Posted by MyronL
Why can't they make a water tank with a clear, see-into-it area so you can do a simple, visual check of the water level?
It doesn't need to be clear. With a flashlight (hold the flashright right against the tank, so you can see the glow coming back out through the tank wall), the water level is visible in typical translucent fresh water tanks. Of course that only works if the tank is exposed (not covered by insulation, for instance), but that would also be true of a clear window.
The usual fix for an obscured (or opaque) tank is a sight glass: just mount a vertical run of clear plastic tube (or hose) in a visible location and at the same height as the tank, connected to the tank at both top and bottom. The level in the tube matches the level in the tank. This doesn't work for waste tanks, as the tube get fouled.
The fresh tank is generally not the problem for stock level systems anyway (since the sensors generally don't get fouled), except that the stock system only has four steps (empty, 1/3, 2/3, full), which is a little vague for some users and purposes.