is it possible to fit a 'watchman' tank alarm/guage to the tank? your local heating engineer should be able to tell you, transmitter is fitted to top inside the tank(i assume ts got a battery in it) and the guage is plugged into a socket inside the house and left switched on it displays a number of bars relating to the oil level. also if the ol level drops faster than (i think more than 2 inches in 24 hours) an alarm sounds indicating either oil theft or possibly a leak. i top my tank up when it drops to 1 or 2 bars.