with the cost of oil your better off replacing the whole line in one using 10mm copper. Replace the isolating valve by the tank. Fit a new filter by the tank a fire valve outside before the line comes into the house and a isolating valve before the flex into the burner oil pump. Last thing you want is to lose all your oil while your not there due to poor pipe work or fittings. Dont use soldered fittings. Should get change from £50.