Tony,
This looks like the right place to ask the question, the horizontal tank is the Bedford's engine fuel. If you are meaning a round vertically mounted tank that is a filter there should be two. The three booms would all be for fuel it is unlikely they would mix it just in case a mechanic put the wrong fluid in the wrong place.
But as always he could be looking at something completely different than I am referring too.
If you look at the Accurate Armour K48003 that shows the fuel tank behind the cab and K48007 shows the filters and the fuel tank has moved, hope this helps.
Don