I have the same issue. Using a 1100 gallon tank for house use and I still unscrew the lid and look down in it. There are a couple of ways to read the level that I haven't gotten around to installing yet, are using clear ridged tubing (polycarbonate is clear and has UV protection) installed into a tee fitting at the bottom of the tank. If you do this be sure to install a valve on top of the tee at the bottom of the tubing. Flip the valve open and read the water level, then close the valve to help eliminate the failure point of the tubing breaking and emptying the tank. The other would be easy to read from quite a distance from the tank. Use a float on the inside attached to a cable run through the top of the tank to a pulley with the other end attached to a weight outside the tank. As you fill the tank the weight will go down and as you use water the float will go down raising the weight. I have seen this done on very large tanks and it works. I hope this makes sense.