CCWKen said:
Most auto parts and rod shops carry senders and gauges that could be adapted to your tank. All you need is the tank depth. Don't try to use a set from a car or salvaged vehicle. These are usually 5-volts and you'll burn it up if connected to 12v.
Wouldn't you need more than tank depth? The shape would be important. My w/b tank is tapered, less width at the top than the bottom. Half of the fuel is deeper in the tank than half the depth. I have thought about this issue too. The simplest is take some time when the tank is empty (or empty is completely during off-season). Measure out fuel in small quantities, e.g. half gallon. Pour into tank, mark the level on some instrument that can be permanently marked and will not dissolve with gasoline. Pour in the next lift (e.g. another half gallon), mark, .... pour, mark, .... pour mark.... In the end, with a full tank, the permanent instrument will have markings unique for the shape of tank on your machine. I know taking a measurement is cumbersome, messy, and subject to getting debris into the tank, but ... better than running out.
If your tank is a regular shape, the linear measuring device should would fine. Maybe there are some electrical senders that can be calibrated for the non-linear tanks.