i would like to monitor a diesel fuel-tank for my poolheater which is controlled with Cayenne with a standard HC-SR04 Ultrasonic module ( http://www.micropik.com/PDF/HCSR04.pdf or http://www.netzmafia.de/skripten/hardware/RasPi/Projekt-Ultraschall/HC-SR04_2.pdf ).
It is cheap, universal and with a simple handling.
Maybe this one could get here in Chayenne!?
There are mouch sample codes on the net.