How much fluid is in the tank???
With this simple to install water level sensor thats not an issue. Its a simple procedure to install, locate a spot that is not very close to a magnetic source (washer pump motor), drill a 23mm hole (just a tiny bit bigger then 7/8) from between 1" to 1 1/2" from the bottom of the tank and above your supply source, insert the sensor into the drilled hole and locate the float arm so that if there was water in the tank the arm would be in the raised position and if empty it is in the lowered position, and tighten down the jam nut = no leaks. This install is very similar to the bulk head fitting......with this you only need to pay attention to the float level arm position so that you get a proper reading.
Heres an image install (notice how the sensor is above the water injection supply fittings)
EDIT 09-13-07: changed hole size to be drilled from 22mm to 23mm