How to connect a capacitive sensor to an arduino?

I need to read theoil level of a tank, and I'm going to use the capacitive sensor like this one

http://www.ebay.com/itm/1-PC-LJC30A3-H-Z-BX-Capacitive-Proximity-Sensor-Approach-Switch-NPN-NO-DC-/181510208507?pt=LH_DefaultDomain_0&hash=item2a42d9fbfb

The problem is that the output goes to the digital input, and to read the level, i would have to read the capacitance, and then the voltage of the sensor.

I don't think there is any way to use this sort of sensor to measure the level, it's designed for 'high enough' and 'too low' only digital output. Perhaps an ultrasonic range measuring sensor could do what you need?

The Arduino Ping sensor looks like it would do the job.