Thanks for that information, the drain point is a simple hexagon form 'bolt' not a valve and I do have the lift pump which you refer to and not a day tank. You mention the 'hand lever on the fuel lift pump', is that the spring loaded lever on the first filter or should I be looking for something else ?
Thank you very much for taking the trouble to reply, it is much appreciated. I will sort out which is the return line although there is what appears to be a 'bleed' screw on the top of the casing.
Mike