Determining how much water I had in my water tank used to be a real chore (what with having to climb the tower in order to peer through the tank’s manhole) … until I devised a painless—yet accurate—way to check the container’s water level while I stood on the ground.
The answer? A simple sight gauge which uses the compression of air in a length of clear plastic tubing as an indication of water pressure … which-in turn-is nothing but a reflection of the tank’s water capacity.
The accompanying drawings will give you an idea of how the system is set up. As you can see, there’s nothing complex about the gauge’s construction (I built mine in two hours at a total parts cost of less than ten dollars … and I’m sure you can do the same). About the only slightly thorny part of the whole project is the calibration of the sight-tube … and even that’s a snap when you know how.
 First of all—with the plug (Part 1) removed from the top of the transparent plastic tube—open the shut-off valve (Part 2) just a crack, until the water level is visible near the bottom of the sight gauge. Close the valve, replace the plug, and tighten the top hosing clamp until air will no longer escape past the end plug. (Hint: Some air loss is virtually inevitable, but you can cut that loss to an absolute minimum by giving the tubing plug a light coat of very thick grease prior to installing it for the last time.)