Typically modern tanks are of plastic construction and have a screw capped filler pipe protruding at the top of the tank and also a plastic capped breather/vent pipe.
In addition there is often a 200mm diameter inspection hatch with moulded ears that allows for padlocking.
The filler pipe and breather/vent pipes have no locking devices thus making the tanks easy targets for the siphoning off of fuel. This fact prompted one Insurance Company, after a spate of siphoning thefts, to state that “it is like having a Tupperware box sitting in the back garden containing £1,000 of cash”.
The design and construction of the modern plastic Oil Tank does not allow for the bolting or welding on of any conventional locking device to the filler and breather/vent pipes.
Older style metal Oil Tanks similarly have screw capped filler pipes and breather/vent pipes but once again do not lend themselves to easy bolting through or welding of conventional locking devices.